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green cliff
Kakagon-Bad River Sloughs, a unique freshwater estuarine habitat. Jim Meeker photograph



Habitat is the sum of all the environmental conditions of a place where an organism or community of organisms live or is most likely to be found. Here the conditions are most favorable for the organism to survive and thrive. Habitats are found within and are part of larger ecosystems, just like a neighborhood may be part of a larger city.

To provide favorable habitat for both plants and animals; the ecosystem must be healthy. These are indicators of ecosystem health in the Lake Superior Basin:

In order to sustain a healthy ecosystem, people living in and using the Lake Superior basin must understand the value of habitat to the plants and animals living here. Habitat in the Lake Superior watershed supports high quality, diverse plant and animal communities. But it continues to change.

The Lake Superior landscape has been modified by historic and current forest use as well as development of shorelines and forested areas. Chemical changes in water and sediments have resulted in degraded habitat conditions for some species and communities. There have been substantial changes in the species composition of some natural communities through the introduction of non-native species.

To understand what makes up the many different habitats with the Basin, we need to know understand the physical and environmental factors that have created and continue to affect both the aquatic and terrestrial ecosystems within the Lake Superior Basin.



Understand the physical attributes that created and continue to influence Lake Superior's habitats and biological communities

Recognize the impact that historic and present day impact land use has on the ecosystem, habitats, and biological communities.

Recognize the diverse and sustainable native biological communities and their habitats within the Lake Superior Basin

Understand how human activities that modify Lake Superior habitats cause stress for some species

Recognize the characteristics of a healthy Lake Superior ecosystem



To understand what makes up the different habitats with the Basin, we need to know understand the physical and environmental factors that created and continue to affect both the terrestrial (land) and aquatic (water) ecosystems within the Lake Superior Basin.

Geologic Influences

geo mapLake Superior's origins date back, about 1.1 billion years, a ancient continent scientists have called "Laurentia" began to split apart. This ancient continent was the precursor to what is now the North American continent. As the two sides tore away from each other, the earth's 25-mile thick crust was pulled like taffy. It became thinner and weaker in the middle forming a giant trough. Part of this trough would eventually become Lake Superior.


presentation1The rift nearly split the ancient continent apart. The tear extended like a arc-shaped scar 1243 miles southwest from the Lake Superior region to what is now Kansas and southeast to lower Michigan. The earth's crust over the rift became so thin that it ruptured causing hot basaltic magma from deep within in the earth to erupt to the surface. Layer upon layer of lava flowed into an ever widening and deepening valley that had formed along the rift.


volcanoHuge volcanoes erupted and flooded parts of the Basin with dark basalt rock. In some places, large mountain ranges were built up, only to be eroded away through the eons that followed. When the eruptions stopped, coarse, sedimentary rocks were deposited on top of the volcanic basalt layers.


The violent activity stopped about 1086 million years ago for reasons not completely known. The dense lava began cooled and the weight of the rock layers caused the rift valley to sink. Eventually the valley was filled in sediments that eroded into it. Today those sediments can be seen as the sandstones of east-central Minnesota and northwestern Wisconsin's Bayfield Peninsula.

Buried beneath a blanket of soil, sand, and rock, the Mid-continent Rift is still here today, like a scar on the face of what we now call the North American continent.

presentation2After this fiery geologic beginning, the Lake Superior region would be shaped ice.

Then the Earth's climate cooled. Temperatures became so cold that glaciers, with ice over mile thick, advanced south from the artic. Glaciers covered the Lake Superior region, only to retreat back north when the earth's climate warmed again. This pattern of glacial advance and retreat occurred several times over the past 2 million years.

The awesome erosive power of mile-thick ice sheets easily ground down the loosely cemented sandstone that filled the core of the old Mid-Continental Rift valley. Like a huge bulldozer, the glaciers gouged away soil and rock, pushing along as they advanced.

The glaciers scooped out what would become the Lake Superior Basin. The tough crystalline igneous rocks forming the flanks of the rift were much more resistant to glacial action. They were not eroded away to the same degree and today mark the edges of the Lake Superior Basin. The exact shape of Lake Superior is directly related to geology of the Mid-continent Rift and the relative erodability of the lavas, intrusions and sandstones contained within it.


When temperature warmed meltwater from the glacier, carried pieces of eroded rock and deposited it along its path in varying thickness. These glacial deposits are called "glacial till.. They are less than 3 feet thick over most of the rocky uplands bordering Lake Superior, allowing some of the ancient volcanic bedrock to be exposed. However, in bedrock valleys or in areas south of Lake Superior, glacial till thickness may average 100 feet and in some places be over 650 feet thick.

The Lake Superior Basin's soils were a direct result of what this glacial action.

The last advance of glacial ice into the region began approximately 115 thousand years ago and ended 10 thousand years ago. As the Earth's temperatures warmed again, the glacial ice began to melt and retreat back north. Melting water filled the scoured-out sandy core of the old rift valley creating a lake precursor of today's Lake Superior. At times meltwater filled the lake to as high as 500 feet above Lake Superior's current elevation of 600 feet.. At other times, water drained from the lake, bringing dropping its level 250 feet lower.

These precursors of Lake Superior are called "post glacial lakes.. Glacial Lake Duluth, 10,000 years ago, occupied an area slightly larger than what is marked by Lake Superior's present shoreline. Unlike Lake Superior, water from Glacial Lake Duluth did not drain out to the Atlantic Ocean, but southward via the Brule-St. Croix valley into the Mississippi River valley. Like a levy, a large barrier of eroded glacial till at Lake Superior's eastern end dammed up its water and prevented it from flowing eastward into the other Great Lakes.

presentation4About 7,300 years ago the barrier was breached, perhaps due to glacially caused flooding. Suddenly the outflow of Lake Duluth reversed. Instead of flowing west and south down the Mississippi River and eventually the Gulf of Mexico; its waters drained east through the other Great Lakes to the Atlantic Ocean.

Several other geologic events followed that caused Lake Superior's waters to rise and fall. It was only about 2,000 years ago that Lake Superior achieved its present day elevation of approximately 600 feet (183 m) above sea level.

Geologic forces that date back to glacial times are still very much at work in the Lake Superior. The enormous weight of mile thick ice that covered the Basin was so heavy it depressed the earth's crust into the fluid molten mantle layer below. When the ice retreated, the earth's crust was released from the great weight. Slowly it began to spring back like a sponge. This effect is called "isostatic rebound.. It continues today at a rate of only a few centimeters a century, but it has significant impact on aquatic habitats within the Basin.

Lake Superior's Sand River Estuary is a drowned river mouth. Photo: Eric Epstein

The northern and eastern Canadian side of the Lake Superior Basin is rebounding faster than the southern and western shore causing the Basin to tip toward the south. Lake water spills onto the southern shore. This is especially important along Wisconsin's Lake Superior coast, where the rebound effect has caused the water to submerge or "drown" river mouths. This creates unique coastal wetland habitats called freshwater estuaries.




Climatatic Influences

Investigate Great Lake marine forecasts and maps.

Lake Superior has a strong effect on the climate of Wisconsin, Michigan and eastern Ontario, but less on Minnesota and the northern part of the Basin. Annual temperatures increase steadily from the Basin's northern to the southern shore.

The lake also has a strong "moderating" effect on climate within a few miles of its shore. Shorelines areas experience cooler summers, but milder winters than inland areas. Winter storms tend to be more intense near the Lake, but the Lake increases stability of the air masses and decreases the intensity of spring and summer storms.

The wettest areas are immediately east of the lake, north of Sault Ste. Marie, Ontario, and parts of Wisconsin and Michigan where there is a strong lake influence. These areas also have the greatest snow accumulation. Portions of the Michigan's Upper Peninsula like Houghton-Hancock average 340 inches of snow; while Duluth, which is outside the zone of greatest lake, influence receives only 53 inches per year.



native shelterNative American Settlement

Centuries ago, the Ojibwa people were drawn to the Lake Superior Basin from the Atlantic Ocean coastal areas seeking the place where "food the grows on the water.. This food was wild rice which grew abundantly along Lake Superior's coastal areas, inland lakes, and rivers. They settled and have lived here since then. Lake Superior's diverse habitats provided many natural and cultural resources they needed. The Lake provided clean water, fish, medicines, and a water highway for transportation. The coastal wetlands and uplands provided plants and animals used for food, materials for shelter, and medicines.

canoe paintThe Native American's impact on the environment was localized to areas where they settled. Family units tended to disperse themselves during winter camps so they would not deplete game and resources in one area. Through hunting, trapping, and some habitat manipulation, Native People influenced the ecosystem, but the impacts were minor compared to what was to come.

Europeans traded European made trade goods for furs harvested by the Native Americans. Picture by Howard Siverton, artist.

The Fur Trade Er.

The first white explorers and settlers were attracted to the Lake Superior basin by the abundance of furbearing animals, especially beaver. The fur trade was big business in the Lake Superior region. Beaver pelts were in high demand in Europe where they were processed into beaver felt top hats, which was fashion for gentlemen to wear. Beaver were all but depleted in Europe, but in Lake Superior's coastal wetlands they were plentiful. The Native people had the technology to harvest the beaver and other furbearers. Europeans had manufactured goods, like firearms, to offer in trade.

An active industry trapping and trading beaver started in the late 1600's and would continue through the 1840's. With the fur trade came the establishment of company fur trade posts and the first permanent European settlements in the Basin. The culture of the Native American people would also be forever changed.

Heavy trapping for trade depleted many populations of furbearing mammals. As these stocks were depleted, the fur trade moved west to more productive areas. Fur trade continued in the Lake Superior region until the 1840's when European fashions changed to silk top hats and the demand for beaver ended.

Commercial Fishing

Lake Superior's once abundant fish populations offered Native Americans a good source of food. As the fur trade industry began to collapse, former fur trade companies looked to the Lake's abundant fish populations as a source of jobs and income. Commercial fishing began in the mid-1800's as the companies like the American Fur Trade Post on Madeline Island switched from furs to fish as a commodity to sell. Overfishing and introduction of exotic species into Lake Superior would lead to the collapse in the Lake Superior commercial fishing industry.

The Bigelow sawmill near Fish Creek on Lake Superior's shore near Ashland, WI, circa 1900

The Logging Era

The Lake Superior Basin's vast forests offered another natural resource. The forest was considered "inexhaustible" and offered a source of wood products needed by a growing nation and income for the logging companies.

Early logging concentrated on white pine; individual trees could reach 200 feet in height and could be easily floated down tributary rivers to sawmills. Red pine was harvested to a lesser extent. Clearing of the ancient forests not only eliminated the forest ecosystem locally and regionally, but it also created other massive problems when cut logs were floated down the closest stream for transport to Lake Superior or other locations. Riparian vegetation was removed, stream banks were trampled, and stream bottoms were scoured or disrupted. The loss of vegetation created erosion of soils and sheet run-off into streams. Water quality was degraded, and fish habitat was lost.

The pines were clear-cut and little was left except slash when the logging companies were done. Once railroads and logging roads were built, hardwood trees could be economically harvested by both clear cutting and high-graded (cutting only the most valuable trees). Hemlock was removed during a later wave of logging when the bark was used for the tanning industry.

wildfireBy the early 1900's the inexhaustible virgin forest was "cut-over." Only scattered trees and dried out slash were left behind. Disastrous fires came next. Fires not only burned the slash, but destroyed remaining trees that could be sources of new seed to regenerate the forest. This significantly reduced the chance that conifer species would regenerate a new pine forest to replace the old one. Hardwood species like sugar maple, beech, basswood, yellow birch, and ash fared better and grew back to dominate the landscape.

In the Canadian boreal forest, logging began later than in the U.S. portion of the Lake Superior basin, mostly because the forest contained fewer timber-quality trees. The trees were harvested mostly for pulpwood.

Today, forest practices have changed, with management strategies focused on a sustainable yield of wood products. Because the Lake Superior Basin's ecosystem is dominated by forest, how they are managed in the future will have a significant effect on the health and sustainability of other habitats. The National Wildlife Federation predicts that the forest product industry is the most likely industrial sector to grow and have an impact on biodiversity and ecosystem health in the Lake Superior basin.

European immigrants came to farm the cutover land, but first they had to deal with the stumps left behind by the logging companies.


The old saying is: "the plow follows the axe.. After the ancient forests were cut down, sections of land were completely clear of trees except for the stumps. Cleared land seemed ideal for agricultural production, even if the soils were better suited to trees rather than crops. European immigrants came to the region to settle and farm. Some were brought here through the false advertising claims of the timber and land companies who sought to profit by selling the land they cutover before moving west to continue their logging practices. Communities and towns grew up around the new agricultural settlements.

However, the advertising claims that this land is being ideal for agriculture were false. Most of the forestlands proved unsuitable for farming. The soils, and climate, were suited to producing tress, not crops except in localized areas. Where farming was done in wetland areas, the land was often drained or filled to promote drainage. Cropping and grazing practices contributed to high rates of erosion off the land and into the steams. Later, some of the most toxic and persistent chemicals used in the mid-1900s were agricultural-based.

cabin familyThese practices contributed to the loss of wetlands, sedimentation, and the contribution of persistent pesticides into the environment. Impacts of these former practices still affect the region.

Today agriculture only dominates about 1% of the landscape in the Lake Superior basin today. The majority of early farms were abandoned and the fields either grew back to trees, were planted to trees, or have become dominated by brush. Only the areas with productive soils remain in agricultural production today, dominating the landscape in localized areas such as the Bayfield Peninsula.


Mining was dangerous work. Some iron ore mines on the Gogebic-penokee Range were almost a mile deep.

The Lake Superior Basin is a mineral rich area. Since the mid-1800s, mining has had a major impact on the economics and natural resources of the basin.

During the 1870s, the Silver Islet mine east of Thunder Bay, Canada was the world's most productive silver mine. It closed in the early 1880s.

"Red Gold" or iron ore was discovered in 1883 on the Penokee-Gogebic Iron Range in Wisconsin and Michigan and mining there continued through the 1960's. Iron ore mining in Minnesota began in 1884 on the Vermilion Range and in 1892 on the Mesabi Range. The eastern portion of Minnesota's Mesabi Iron Range is within the Lake Superior Basin. Mining of taconite, a lower-grade iron ore, continues on the Mesabi Range, and Minnesota remains the largest producer of iron ore and taconite in the United States.

The Lake Superior Basin is also rich in copper. The Keweenaw Peninsula in the Upper Peninsula of Michigan was the world's leading producer of copper during the early 1800s. Today it is one of the largest Superfund sites in the United State, called the Torch Lake Area of Concern. This toxic site is a result of widely scattered deposits of toxic copper mining waste materials accumulated over more than 100 years of mining, milling, smelting and recovery activities. The White Pine Copper Mine, located in Michigan's Upper Peninsula, both extracted and smelted copper ore. It was a significant source of toxic pollution before it ceased operations in the late 1990's.

Brownstone is a special type of sandstone that was used as a building construction material. It could be easily shaped into decorative building facades, yet it was strong an durable. Brownstone is found along Lake Superior's shore and on the Apostle Islands. In Wisconsin, brownstone was quarried in the late 1800s to early 1900s. Approximately 12 quarries were mined, and the brownstone was exported to large cities in the United States, including Chicago, St. Louis, and Minneapolis/St. Paul. Brownstone buildings remain in the basin in Wisconsin, but brownstone is no longer quarried. Old, unreclaimed quarries dot the landscape.


skiersThe forests, streams, and lakes of the Lake Superior basin have attracted outdoor recreation enthusiasts throughout the 20th century. Since the mid-19th century, resorts and lodges have housed visitors from metropolitan areas who come for hunting, fishing, boating, camping, and other outdoor pursuits. Outdoor recreation interest remains high today and is increasing in popularity, especially in areas within driving distance of metropolitan centers, such as Minneapolis/St. Paul, Milwaukee, and Chicago. Recreation pursuits have expanded to include skiing, snowmobiling, all-terrain vehicle riding, hiking, bicycling, wildlife watching, sailing, and others. Both public and private Facilities for these activities have been developed in response to the interest and need.



Population Change

population map
Population centers can be seen at night from satellite imagery. The red line marks the Lake Superior Basin boundary.

From pre-European time to today, most human habitation and urban structure is on or near the Lake Superior shoreline and coastal areas.

The largest communities in the basin— Duluth, Superior, Marquette, Thunder Bay, and Sault St. Marie—are located directly on Lake Superior. Shoreline development continues today, but the focus has changed from industry toward housing and recreational development. This development creates more roads and infrastructure, hardens shorelines by introducing man-made structures, and causes a loss of vegetation.

The 1995 human population of the Lake Superior is estimated at 607,121 people.

Most of the basin is sparsely populated. Most of Ontario and the Minnesota north shore has less than 2 people / 1.2 sq. miles or 2 km2. Population density is greater on the on the south shore of the lake. Population centers are the larger cities of Thunder Bay, Ontario Duluth/Superior Minnesota/Wisconsin, and Sault Ste. Marie, Canada.

population change map
Population change between 1991-1996

Most of the basin experienced a small increase in population (0 – 5 percent) between 1991 and 1996. The greatest population growth was on the Minnesota north shore into neighboring Ontario, the Keweenaw Peninsula, and the area west of Sault Ste. Marie Michigan. The population density in most of these areas still remains low.

Other areas with increasing populations include the Minnesota-Wisconsin's Duluth/Superior area and Wisconsin's Bayfield Peninsula. Access to quality outdoor activities and a booming real estate market has influenced land sales and land and home acquisition. The trend of private owners buying land and/or second homes/cabins is increasing, especially near Lake Superior and on inland lakes. In the United States, this trend is greatest along the North Shore of Lake Superior because the areas is within a half-day drive from large metropolitan areas like the Fox River Valley, Twin Cities, and Milwaukee-Chicago.

Shoreline habitants both upland and aquatic can lose much of their biodiversity as they become developed.

This increased demand for land, especially along rivers and lakeshores, creates further stress on the landscape and habitats. Subdividing larger forested tracts into smaller pieces for second home development fragments forest ecosystems. Shoreline development can break up habitat continuity along rivers and lakes.


By the early 1830s, the Great Lakes were opened to international shipping with the completion of several canals that connected all the Great Lakes to the St. Lawrence Seaway. The Lake was a great water highway, especially well suited for the transportation of heavy commodities like iron ore to be more efficiently transported by ship.

shipThis allowed commodities harvested from the Lake Superior Basin to be exported to growing cities farther east. Shipping was a growing industry in many Lake Superior cities in the late 1890's and early 1900's. Today, only a few major shipping docks remain, including those at Duluth-Superior in the United States, and at Thunder Bay, Marathon, and Sault Ste. Marie in Ontario. Declining amount of heavy commodities like iron ore and more reliance on overland transportation by truck and rail, have reduced shipping.

Railways created additional accessibility and were important for transport of harvested hardwood timber, which was not readily transported by water. Numerous railroad companies and railroad spurs were prevalent in the late 1800s and early 1900s, providing transportation to and from the region. Today, most railroad lines within the US side of the Basin have been abandoned, except for a few freight lines that service industries within the largest cities.

Since the 1950's, the emphasis has been focused on highway transportation. Highways serve industry, commercial, and tourism development interests. They have "opened" the region to more visitors who reside in larger urban areas and can now reach the Basin within less than a day's drive. Transportation construction and improvements affect habitats and the species that live there from construction practices, encroachment into natural areas, and vehicular use.

Political Boundaries

The Lake Superior basin is divided between two countries, three states and one province, and several sovereign Native American tribes and First Nations.

native americans drawing
Artist drawing of early treaty signing.

Native Americans have lived in the Lake Superior Basin for thousands of years. Through a series of treaties and agreements, they ceded some of their original land holdings to the US and Canadian governments. US tribal reservation lands and First Nation reserve lands were established within the Lake Superior Basin and make up less than 1% of the land base.

Treaties with tribes like the Ojibwa ceded land, but not other hunting, fishing, and gathering rights, to provincial or federal governments. Investigate more about Canadian treaties and US treaties

Each of the states is divided into counties, including 7 counties in Minnesota, 5 in Wisconsin, and 11 in Michigan. The two districts in Ontario have no elected bodies or land management authority. Tribes are sovereign nations with their own governmental structures.

habitat mapHabitat types, and the plants and animals associated with them, do not recognize political boundaries. However, environmental management regulations and philosophies can vary greatly between countries, tribes, and local units of government. A challenge is to coordination habitat management across political boundaries.

One of the unique characteristics about the Lake Superior basin is that much of the land is in public ownership. Today in U.S. portion of the Basin, approximately 54 percent of the land base in the basin is privately owned, compared to 90% in Ontario. In the US, the Basin's public land held by various federal agencies including the National Forest Service, National Parks Service, and the US Fish and Wildlife Service, state government and Departments of Natural Resources, and county governments in Michigan, Minnesota and Wisconsin.

glossary maplake mapPublic ownership provides varying degrees of protection for specific sites and habitats, which may be managed for forestry and recreation, as well as providing some wilderness representation depending on the management mandate of the agency or tribe administering the land.

legacy map
Investigate Ontario's Living Legacy Areas.

In the last few years significant steps have been taken to increase the number of areas under protection around the lake. "Ontario's Living Legacy" has identified many new areas for new or additions to existing parks. In Canada, policies are being developed to designate recognize the Great Lakes Heritage Coast. This policy will recognize the "internationally significant natural, cultural, scenic, and recreational values of the Lake Superior shoreline..

Even with the increase in the number of protected areas there are still areas that need to be considered. World Wildlife Fund Canada (1999) concludes "... there remain significant gaps in the core protected areas system for the Lake Superior basin in both the terrestrial and aquatic portions, and both in the United States and Canada..

conservation map
Investigate a new proposal called the "Lake Superior National Marine Conservation Area" to protect the lake's natural and cultural heritage.


map morphology
Keweenaw Peninsula: Investigate more about Great Lakes bathymetry.


Lake Superior is more than just a big bathtub filled with cold water. It is a complex aquatic environment with special communities of plants, fish, and animals that use its many watery habitats.

To understand more about the aquatic communities, it is important to know more about Lake's water that influences them.


Bathymetry and Basin Morphology

Our word "bath" comes from the word "bathymetry" which means the measurement of the depth of bodies of water. Lake Superior averages 482 feet (147 m) in depth with a maximum depth of 1332 feet (406 m) The Keweenaw Peninsula, sticking out into the lake from the southern shore like a beak, divides the Lake into three underwater bathometric basins.

earthThe eastern basin is characterized by a series of long, parallel, steep-sided troughs that are oriented north-south.

The central basin is comprised of very deep (up to 1332 feet or 400 m), steep-sided sub-basins bounded on the north extensive underwater cliffs, which fringe a complex series of islands.

Lake Superior's shoals have claimed many ships.

The western basin encompasses relatively shallower offshore waters and a very deep channel, the Thunder Bay Trough, which separates Isle Royale from the adjacent mainland.

Water depths of less than 300 feet (100 m) are found in a narrow band paralleling the shore, with a rapid fall-off to deeper waters. Water depths of less than 300 feet are also found around islands and off shore shoals, especially in eastern Lake Superior. Shoals are numerous along the eastern shore and northern shore.

Sediments and Sedimentation

Erosion from Fish Creek washes red clay sediments into Lake Superior's Chequamegon Bay.

Sediments are solid fragments of inorganic or organic material that come from the weathering of rock and are carried and deposited by wind, water, or ice.

red clay in water
Red clay suspended in lake water.

Sediments found in Lake Superior are a result of its glacial past and post-glacial activities, especially human land use. Most of the existing sediments in Lake Superior Basin were deposited about 10,000 years ago when the last glacier bulldozed out the lake's drainage basin and left behind red clay.

Red clay is a common component of lake sediments especially in the southwestern portion of the Basin. When eroded into the Lake, these sediments can stay suspended in the water column for a long time. Red clay sediments, washed into the Lake from shoreline erosion or tributary rivers, give the water a telltale red color. Modern sedimentation rates approximately 6 million tons of fine sediment annually. In some areas, like the Fish Creek Estuary near Ashland, WI, sedimentation rates today are greater now than before European settlement of the area due to changes in land use.

shore ersosion
Shore erosion effects both the Lakes' water quality and human health and safety.

Shoreline erosion is the largest external source of sediment that erodes into the Lake. The red-clay region on the western shore of the Keweenaw Peninsula contributes up to 58 percent of annual sediment load going into the Lake.

The Nemadji River, near Superior, WI, carries significant amounts of red clay sediment into Lake Superior.

Lake Superior tributaries are the second most important source of sediments with 30 percent of total sediment load into the Lake. Some sedimentation is caused by the natural erosion of red clay soils. Some of this erosion can be accelerated by poor land use practices.

Sedimentation can come from industrial sources. Erosion from taconite tailings in Silver Bay, Minnesota account for 7% of the fine-grained sediment goin. into Lake Superior. These particles are significant because of their high concentrations of toxins and nutrients.

Waste rock "tailings" piles left over from mining operations at Silver Bay, MN.

The Lake's circulation patterns help keep the suspended clay particles in areas like the Duluth basin and western shore of the Keweenaw Peninsula. Approximately 37 percent of the current natural sediment load is deposited in the Duluth basin

When sediments are washed into the Lake, they can affect negatively aquatic habitats by:

-Reducing the amount of light penetrating the water, depriving the plants of light needed for photosynthesis.

-Absorb warmth from the sun and thus increase water temperature. This can stress some species of fish.

-Bury and suffocate fish eggs and bury the gravel nests they rest in.

- Dislodge plants, invertebrates, and insects in the streambed. This affects the food source of fish, and can result in smaller and fewer fish.

-Decrease the penetration of light into the water. This affects fish feeding and schooling practices, and can lead to reduced survival.

map elevation
Lake Superior Current Patterns

Water Current and Circulation

Currents are affected by wind conditions and internal pressured caused by density variations and the slope of the thermocline.

In Lake Superior, both surface and deeper water currents generally flow parallel to the shore in a counter-clockwise direction. There are also smaller subcurrents created by the Lake's bottom topography, temperature and local wind conditions.

upwellUpwelling occurs where sub-surface water is brought to the surface of the lake to replace surface water that has been forced to move laterally by wind or the temperature-density pressure gradient. During the summer, surface water tends to flow away from the near shore upwelling zone along the north shore of Lake Superior and towards the near shore downwelling zone along the southern shore.

Upwelling is important because it brings nutrients and organic matter from the lake bottom and deeper waters up into more biologically active surface waters, which tends to increase their productivity.

Water Level Fluctuations

Lake Superior's water levels undergo natural variation at the short-term, seasonal and year-to-year cycles.

Seasonal changes in water levels occur in response to the annual cycle of precipitation and runoff. Lake Superior's levels typically peak in October and recede over the winter, reaching the lowest levels in early spring, followed by a steady rise through the spring and summer.

The seiche is constantly wetting and dying Lake Superior's fresh water estuaries.

Lake Superior has unique phenomena resembling a tide although it is not related to lunar cycles. It is called a "seiche" (pronounced "say-esh"). A seiche is an oscillation that moves back and forth in lakes, bays, or gulfs from a few minutes to a few hours as a result of atmospheric disturbances. Like a soup in a bowl, Lake Superior's water sloshes back and forth driven by wind and changes in barometric pressure across its large Basin causing seiches.

A seiche is most noticeable in coastal wetland areas where the water levels may raise or fall by a few inches to over 3 feet in less than an hour's time.

Seiche activity can influence the composition of the fish community simply by delivering oxygen to renourish coastal wetland backwaters that can become low enough in oxygen to discourage fish.

Water level fluctuations are important in maintaining healthy wetlands and estuaries. Extreme low water levels allows cyclic, renewal processes such as oxidation of sediments and germination of submerged seed to occur along the shoreline. High water levels prevent the trees and shrubs from growing into open wetlands. Plants and animals who use these coastal wetlands habitats must be adaptable to these wate. fluctuations.


Lake Superior is the COLDEST of the great lakes.

Water temperature is critical to the entire Lake Superior ecosystem. It affects rates of chemical and biological processes and influences patterns of currents, and mixing of water with the Lake.

Lake Superior is COLD! It's unique temperature structure is due to its size and depth. Superior has the lowest summer surface temperature 55-degrees F (13°C) and mean annual lake temperature 38.4-degrees F (3.6°C) of the Great Lakes.

stratLake Superior alternates between periods of stratification during summer and winter and of extensive vertical mixing in spring and fall. This typical of dimictic lakes

During winter the coldest water is actually closer to the Lake's surface. The colder waters of the epilimnion (the top layer) rest on denser, warmer water below. In April the Lake reaches its lowest mean lake temperature of 34.5-degrees (1.4 ° C). The water stratifies into different temperature layers. Thermal stratification prevents the water layers from mixing together.


summer strat

winter strat



Investigate more about lakes stratification and mixing.


In the spring the water warms rapidly. Once water temperatures from the Lake's surface warm and become the same as the bottom layers, the Lake is no longer stratified. Now water within the Lake is free to circulate from top to bottom mixed by the wind. This circulates nutrients and oxygen through the Lake.

By mid-July, surface waters have warmed past 39-degrees F (4°C) across the entire lake and summer stratification occurs.

As surface temperatures rise rapidly under the summer sun, a thermocline develops. This is a line where the temperature of the water changes. The thermocline separates warmer water above and colder waters below. The thermocline acts like a barrier stopping heat being transferred downward and it preventing mixing of the warm epilimion top water layers with the colder hypoliminion layer below. Temperatures in the hypolimnion will remain fairly constant throughout the summer at a chilly 39-degrees F (4° C).

august temperatures
Mean August surface water temperature for Lake Superior.

Surface temperatures continue to rise, reaching a maximum of approximately 55-degrees F (13°C) by September. Water temperature can be significantly higher in sheltered bays and shallow coastal areas creating warmer water habitats.

Beginning in mid-September, surface waters start to cool again until the Lake achieves the same temperature top to bottom. Once again, mixing can take place again and will continue until surface water temperatures drop and the Lake stratifies for the winter.

Ice Cover

Normal winter maximum ice cover for Lake Superior shown in pink.

During most winters, the lake is 40 to 95 percent covered by ice. Wind usually keeps the center of the lake open. It occasionally freezes over completely. Maximum ice cover normally occurs in late March. At this time, most of the shallow bays and along much of the north shore are completely frozen over.

Ice cover has important environmental impacts. It provides insulation between the atmosphere and relatively warm water, thereby reducing heat loss, evaporation, and the occurrence of lake-effect snowstorms. It may also impact upon fish reproduction.

Ice cover affects and dispersal of terrestrial mammals to islands, such as caribou and wolves who can travel over the ice pack with ease. This allows them to extend their winter range and sometimes migrate to new habitats.

Water circulation has a strong impact upon ice cover. Midlake upwelling keeps the central area of the Lake free of ice and is responsible for the lack of ice along the open part of the northwest shore.

Water Chemistry

The water chemistry of Lake Superior is determined by the geology and climate of its drainage basin, anthropogenic inputs, bottom topography, circulation patterns, thermal regime, and biological processes.

Lake Superior is classified an ultra-oligotrophic lake. An oligotrophic lake is very low in nutrients, and has a large amount of dissolved oxygen due to its cold temperature.

For most of the year, Lake Superior is saturated with dissolved oxygen. In the spring and fall, when the lake mixes, nearly all of the Lake water is exposed to the atmosphere and as the lake "turns over".

Lake Superior is characterized by high concentrations of total nitrogen, but very low concentrations of total phosphorous. This limits the Lake's productivity for fish and plant life. This is true throughout the Lake, except in areas where water circulation is restricted or near urbanized areas like Duluth MN. Here elevated levels of total phosphorus and silica from man-made sources like industrial, agricultural, and homes can runoff into the Lake causing increased nutrients levels.

Chlorophyll a concentrations are a measure of phytoplankton biomass such as algae. Higher chlorophyll a levels indicate that there is higher amounts of nutrients in the water available to stimulate algae and biomass growth. Generally chlorophyll a levels are low throughout the Lake Superior, only increasing near coastal communities where there is more nutrients inputs into the water. Lake Superior'. low chlorophyll a levels means that there is very little algae or biomass in the water column making it very transparent. In some places it possible to see to depth of almost 100 feet.



Nearshore Habitat and Embayments

cheq bay
Chequamegon Bay

Nearshore open water habitat consists of areas where the water depth is less than 262 feet or 80m. Embayments (or bays) are partially enclosed by land and therefore less exposed to wind and wave energy. Together, these habitats make up about 20 percent of Lake Superior's surface area.

Nearshore waters consist of a narrow band along the north shore and a generally wider along the south shore. The most extensive areas of nearshore habitat are at the east and west ends of the lake. Nearshore habitat is also found around Isle Royale and other islands and includes offshore shallow waters, such as the Superior Shoal and the Caribou Island Reef Complex. Major embayments include Black Bay, Nipigon Bay, Thunder Bay, Batchawana Bay, Whitefish Bay, Keweenaw Bay, and Chequamegon Bay.

Nearshore areas are important because they are more diverse and productive than offshore waters. Most of Lake Superior's fish species use nearshore waters at some stage of their life cycle. Many commercially important fish use nearshore waters exclusively. Nearshore habitats have warmer temperatures and greater diversity of substrate types than offshore areas. In exposed stretches, waves and currents clean the substrate of sediment, maintaining suitable spawning and nursery habitat for fish species. Aquatic vegetation, needed for food and cover, is found only in nearshore habitats.

Some of these sites are especially productive, support exceptionally high biodiversity, support rare species or habitats and contribute significantly to the integrity of the whole ecosystem.

Loss of fish and wildlife habitat occur primarily in the nearshore zone. Nearshore habitats, especially bays, are receive more impacts of human activities than offshore areas.

Sawmills like this one at the head of Chequamegon Bay dumped sawmill waste into the Lake.

Some nearshore Lake Superior waters have an accumulation of sawdust and woody debris associated with log drives and sawmills in the late 1800's and early 1900's, degrading spawning habitat for fish. Embayments are also impacted by dredging, dumping of dredged material, and thermal loading. Exotic species, such as purple loose strife and ruffe can degrade the nearshore habitat.

Eutrophication, caused by nutrients input from sewage plants, industry and agriculture. The nutrients act like a fertilize and stimulate the excessive growth of algae. High algae concentrations limits underwater visibility and uses up oxygen needed by other aquatic life. On Lake Superior, eutrophication is a local problem on some bays, but algal mats have been discovered covering isolated rock shoals in Lake Superior.

Offshore Habitat

This is deep water habitat is below 262 feet or 80 meters. This habitat makes up about 80% of Lake Superior's surface area.

Offshore habitats are less productive and diverse than nearshore habitats. There are only a few species of deep water and bottom-dwelling fish here. The benthic habitat is dark and has a constant temperature of 39.2-degrees o. 4oC.

Offshore habitats in Lake Superior are generally regarded to be healthy. Dumping or discharges from vessels may threaten habitat, but the impacts are not well understood.



Microscopic phytoplankton

Lake Superior's aquatic communities occupy three major trophic levels, each having its own cast of species. Energy captured from sunlight by phytoplankton flows upward from one trophic level through a complex food web. Biological production generally decreases about tenfold from a lower trophic level to the next higher level.

Phytoplankton Community

Phytoplankton are microscopic free floating aquatic plants. We often think of them as "algae", but the community represents an approximately 300 species. One type of plankton, called Picoplankton are so small that 500,000 of the fat ones can fit on the head of a pin!

Phytoplankton are extremely important since they are the first step in the Lake Superior food chain. Like most plants, they can convert the sun's energy into biomass. These tiny animals, bacteria, and plants floating in the Lakes are then eaten by fish and other aquatic animals.

Most of the Lake has very low phytoplankton biomass and this characteristic is the reason why the lake is classified as an ultra-oligotrophic lake. The exception is nearshore areas where concentrations of phytoplankton are be higher due to higher nutrient levels, often caused by human activities.

Zooplankton Community

Like phytoplankton, zooplankton are also microscopic, but they are animals and not plants. Zooplankton eat phytoplankton and in turn are eaten by baby fish. Distribution and abundance of zooplankton is strongly associated with surface water temperature. The highest concentrations are found inshore, especially in the major embayments. Their abundance is generally low in comparison with the lower Great lakes.

Benthic (Bottom) Communities

The "scud" is a member of Lake Superior's benthic community.

Sediment size, depth and therefore temperature are the major factors controlling the distribution of individual species. In deep water communities, mollusk and insect populations are extremely scarce. Benthic invertebrate communities are well suited for use as biomonitoring tools, because the various benthic organisms have differing sensitivities to environmental stressors. By measuring the diversity of the benthic community, we can gain some insight into the level of human impacts on the aquatic system.

Fish Communities.

Coaster brook trout

The native fish community of Lake Superior was and is still dominated by salmon, trout, cisco, and whitefish. Approximately 80 fish species belonging to 19 families occur in Lake Superior or its tributaries. Of these, twenty species are non-native that have been deliberately introduced such as chinook salmon and rainbow trout.

Historically, the fish community of the main lake was comprised of lake trout, whitefishes and ciscoes, burbot, sticklebacks, sculpins, and suckers. Lake trout, and to a lesser extent burbot, were the dominant predators. Today, the predator mix has been expanded by the introduction of non-native salmonines like the chinook salmon, but lake trout remains the dominant predator. Lean lake trout, steelhead, coho and chinook salmon are most abundant in nearshore waters less than 262 feet or 80 meters depth. Brown trout and splake are less widely distributed than other naturalized salmonines.

silver fish
Coasters are being reintroduced into Lake Superior's Chequamegon Bay at the Whittlesey Creek National Wildlife Refuge.

Coaster brook trout were formerly more abundant in nearshore areas but have been reduced by overfishing, competition with introduced species and destruction of spawning habitat in tributaries.

The main forage or "food fish" for lake trout historically was lake herring. The non-native rainbow smelt has become another forage fish species.

The fish community found in bays, harbors and estuaries is typically perches, suckers, sculpins, and minnow species. Walleye is most abundant in mesotrophic waters less than 50 feet or 15 meter in depth, although they may be found deeper. Both walleye and lake sturgeon were formerly more abundant and exist mostly in localized populations. The recent introduction of exotic river ruffe, white bass and round gobies may have profound impacts on these warmwater communities by moving into habitat used by native fish and competing with them for food.

About 20 fish species, such as catfishes and sunfishes, are restricted to the warmest weedy shallows of protected bays and estuaries. Tributaries and freshwater estuaries are critical spawning and nursery habitat for many species, including walleye, sturgeon, burbot and salmonines. Minnow species, native lamprey and the central mudminnow are generally confined to tributary waters.

Changes in the Fish Community

In the mid-1800's, commercial fishing for lake whitefish (Coregonus clupeaformis) and lake trout (Salvelinus namaycush) began as a way to provide food for fur trading posts and other settlements. By the late 1800's, increased human population, improved transportation, and the decline in fur trading made commercial fishing a growing industry. Better boats and gear resulted in a more efficient harvest.

lamprey on fish
Eel-like lamprey attached to a lake trout. (USGS photo)

The most accessible fish populations were heavily fished until that population declined, then efforts switched to another location or species. Records of depleted stocks date back as early as the 1870's and there was a general pattern of decline for many commercial species between the mid 1940's and early 1970's.

Overfishing was bad enough, but the migration of predatory sea lamprey into Lake Superior in 1938 almost wiped out the already declining populations of lake trout, burbot, whitefish by the 1950's. During the time of highest sea lamprey abundance, up to 85 percent of fish not killed by sea lamprey exhibited sea lamprey wounds.

Commercial fish yields from 1979 to 1983 in Lake Superior sharply dropped. Even today, lake herring and lake trout populations have not yet fully recovered. Recreational fishing has had less impact on fish populations, but contributed to the decline of some populations of lake trout and brook trout, especially in shallower waters. Since 1983, lake herring have produced larger year classes and most lake trout stocks have been restored. Regulation of commercial fishing, closures on fishing, and aggressive on-going sea lamprey control has helped stablize lake trout and other fish population.

The accidental introduction of aquatic invasive species such as the ruffe, and rainbow smelt; commercial and sport fishing pressure; the introduction of non-native sport fish species, and changes in the physical environment such as dams, have made the Lake's fish community somewhat different and less stable than it was in the mid 1800's.

Lake Superior's fish community has been permanently altered by aquatic invasive species and remains at risk from further introductions. To make progress in restoring the lake and its native species will depend on successful control of the sea lamprey and other aquatic invaders, which requires continuous and expensive intervention. The good news is that despite these challenges, Lake Superior's fish community is reverting to a more natural state resembling historical conditions and requiring less management intervention and control.



The Relationship Between Plants and Animals

Green plants form the base for all animal life. The protection of plants in the ecosystem is connected with the protection of the wild animals species. In the Lake Superior Basin the number of endangered plants far exceeds that of wild animals. For every threatened animal there are two or more endangered plants. The importance of plants to the survival and well being of wild animals is critical.

forest area
Forested area within the Lake Superior Basin (in green shades) dominate the region's landscape.

Ecological land classifications are land units that differ significantly from one another in their physical and biological characteristics. There are 37 different land classification units within the Lake Superior Basin each with different relationships between vegetation and the physical environment, especially soils, landform, and climate. Each provides different habitats for wildlife.

Forests vegetation dominates the Lake Superior Basin and represent the largest land class. Approximately 88% of the land with the Lake Superior Basin is either in conifer or hardwood forest or a mixture of the two types. An additional 1.3% are early successional stage or "seral" hardwoods. Only 4.5 percent is classed as grass or brush. The majority of the forests are managed under government jurisdictions for multiple use (to provide wood products, wildlife production, recreation, and other benefits) or as industrial timberlands.

Only about 5 –8% of the Lake States forest is presently "old-growth". Old growth" is used to describe forest ecosystems with old trees and their associated plants, animals, and ecological processes.

old growth"Old growth" is dominated by long-lived species including red and white pine, oaks, northern hardwood species, and lowland conifers. The age at which this occurs depends on species composition, site variables, and stand conditions, but is approximately at 120 years for long-lived species. These forest are called the "primary" or "virgin" forests because they were established naturally and show little or no evidence of human disturbance. Forests that experienced human-caused fires or logging long enough ago and have recovered to near natural state may also be called "old growth."

Today only about 1% of the presettlement primary forest remains in the Lake States compared to an estimated that 68 % that existed prior to European settlement.

The Porcupine Mountains is largest old growth northern hardwood forest in North America and is closest to pre-European settlement condition of any upland forest remnant in the Great Lakes region.

The forest on the southern portion of the Basin is made up of mixed hardwood stands, pure stands of aspen or pine especially on industrial forestlands, and some islands of boreal forest. Most of the Canadian side of the basin is boreal forest.

Threats to Forest Communities

Two major disturbances naturally occurred in the forests of the Lake Superior basin. In the hemlock and hardwood forests in the U.S. side of the basin, fire was relatively rare and the major disturbances were caused by heavy or catastrophic windstorms and tornadoes that leveled trees.

Fire is the most important disturbance in the boreal forests and pine forests Basin's northern areas. Lightening was typically the cause of fires historically. Fire is essential to the regeneration dynamics of most boreal forest species, particularly early successional species such as jack pine.

The extent of fires in each decade has decreased steadily within the basin as a result of a more aggressive policy of fire suppression, combined with improved detection and fire-fighting methods.

Spruce budworm has become the most important forest pest in the Lake Superior basin in terms of total area infested, length and frequency of outbreaks, as well as volume and numbers of trees killed. It attacks primarily balsam fir, followed by white spruce, and to a lesser extent black spruce. Affected trees will die if exposed to 3-5 years of consecutive years of defoliation, and almost all the trees in dense, mature balsam fir stands can be killed during uncontrolled outbreaks. Spruce budworm outbreaks are very large-scale phenomena and usually consist of many infestations that occur in different localities within the basin at about the same time.

Windthrow, or trees falling over, is relatively common in boreal forests, and is the other major natural disturbance in the Lake Superior basin. Shallow-rooting species such as white spruce and white pine are particularly vulnerable, as are forests heavily affected and weakened by spruce budworm.

Vegetation change scenarios predict global warming could alter forest composition so that the shores of Lake Superior will feature more southern species of trees (oaks and maples) or even prairie - if these plants are able to adapt to the different soils and day lengths found in the northern climes.

Pioneer tree species, like aspen, prefer open sunny environments and cannot grow well in the shade of other trees.


Is the natural replacement of different trees species in a forest until the climax species or the final dominant species is achieved. Species such as jack pine, white birch and trembling aspen are called "pioneer species" because they are sun lovers. They cannot tolerate growing in shaded areas, like underneath other trees.

They are often the first tree species to grow in an open area where there is plenty of sun for them to bask in. As long as these pioneers can form vigorous, fully stocked stands, they restrict the shade tolerant trees from invading and growing up underneath them. However, once more shade tolerant species such as white spruce and balsam fir seedlings may become established they can grow in the pioneer's shade and eventually shade them completely out. If there is no fire or another disturbance that would set succession back and reopen the forest canopy to sunnier conditions, shade-tolerant species will eventually dominate the forest. In boreal forests the climax species include balsam fir or black spruce on wetter sites. In the more temperate forests on Lake Superior's southern shore, they are sugar maple, yellow birch, and hemlock.



The Lake Superior Basin represents transition zone for wildlife. Like a cross roads, many species that live here represent animals populations common in ecosystems found in northern southern, eastern, and western areas of the US and Canada.

There are 59 species of mammals native to the Lake Superior basin. These species have wide-ranging distributions patterns. Approximately 1/4 of the Lake Superior's wildlife species are common to northern boreal forest, 1/5 to southerly deciduous forests, and remaining species are common to either eastern or western regions.

Lake Superior is a huge waterbody that poses a physical a barrier to wildlife dispersal. Differences in forest composition and climate around the Basin also limit how much species can diverse. Only 2 vertebrate species, the kiyi (Coregonus kiyi) and the blackfin cisco (C. nigripinnis), are endemic or unique to the Lake Superior Basin. All other species can be found in other environments.

Wild turkeys are among the most recent wildlife species to be introduced by game managers into the Wisconsin counties along Lake Superior's southern shore.

The fauna of the Lake Superior basin has changed since the last Wisconsin glaciation, especially in the past several hundred years as a result of over-hunting and habitat change. The biggest habitat change has been the loss of unfragmented and older successional forests. This has significantly affected the types and distribution of wildlife. Species like the woodland caribou, wolverine, cougar, and grey wolf that need these conditions have been greatly reduced in abundance and distribution, particularly in the southern portion of the basin. A few species such as white-tailed deer and the coyote have benefited from these habitat changes and expanded their ranges and numbers.

Many game species, predators and furbearers such as the moose, black bear, river otter, bobcat and beaver were exterminated in the Basin near the turn of the century due hunting and trapping. Their numbers have recovered to some degree, although not to pre-European settlement levels

Because many wildlife species have been harvested for food and pelts, we have seen dramatic changes in community structure and abundance. The animals that are of interest to trappers and hunters tend to be managed to their harvestable populations, not on their impact on the overall ecosystem. Society views these species primarily for their value to humans, not for their value as a functioning part of the ecosystem.

Ungulates (hoofed mammals)

deerWithin the Lake Superior basin and surrounding area, the original ranges occupied by large ungulates have been substantially altered from pre-European settlement patterns. Harvesting, human disturbance, and habitat changes have nearly eliminated woodland caribou and elk. Elk have been reintroduced into northern Wisconsin, but they are found nowhere else in the Basin.

Woodland caribou historically ranged throughout most of the Lake Superior Basin, but now are only found in the northern edge of the basin in Ontario and in remnant populations on islands and in parks. Hunting, fire, land clearing, logging, increased predation, disease, and human disturbance have caused a decline in their numbers. In Ontario, timber harvest following European settlement provided an abundance of woody browse, which favored moose and deer populations. More moose and deer encouraged a population increase in wolves, a natural predator. As wolf populations increased, caribou populations came under greater predation stress. Caribou and moose cannot co-exits with white-tailed deer on the same land base because deer carry a parasitic disease called "brain-worm" that does not affect them, but is fatal to caribou and moose.

deer signIncreasing numbers of white tail deer caused several negative impacts to the ecosystem especially to plant species and plant communities. Deer browsing can affect the natural regeneration of plant species, especially of plants they prefer to eat like hemlock. Over populations of whitetails can actually manipulate the number and types of plant species may suppress natural forest regeneration. This effects the entire forest community and has been shown to can affect habitats for canopy nesting birds and insects,


Furbearers and Predators

Beaver, river otter, American marten, bobcat, fisher, mink, and other furbearers were intensively trapped in the mid- to late-1800s, some to the level that they were exterminated from significant portions of the basin. Fishers disappeared from Wisconsin and Michigan due to overharvest and habitat destruction. They have since been reintroduced. Raccoon, fisher, American marten, red fox, and black bear populations have all recovered substantially.

Wolves crossing the Lake Superior ice pack near Isle Royale.

The gray wolf was recently de-listed as a federally endangered and is now considered "threatened". It has no special designation in Ontario or Canada. Recovery programs have been initiated in all three states, and recovery goals are nearly met.

Beaver is one species that impacts both the terrestrial and aquatic ecosystems of the basin. When beaver knaw down trees and build dams, they change the aquatic community structure and open riparian canopies. This is beneficial to some species and a negative to others. Beaver activity can be a negative to cold-water migratory fish communities. Beaver dams create a barrier for cold-water fish trying to move up tributary streams to reach their spawning beds. The water temperature of streams back up by beaver dams can be warm enough to negatively affect cold water species. Even the trees and brush removed by the beaver for food and dam making purposes allows more sun to warm the stream and negatively affect trout habitat.

Small Mammals

Small mammals include mice, voles, bats, cottontail rabbits, and snowshoe hares. Little population information is available for any of these species, except perhaps on a site-by-site basis. This group of mammals plays a very important role in providing a prey base for other mammals and birds and for preying on invertebrates.


Lake Superior is dotted with islands that provide important habitat for migratory birds, including shorebirds, songbirds, and raptors. A special benefit to birds is many of these habitats are managed as national parks or protected in some way. They also provide an environment that is different from mainland habitat. They require special consideration in research, management, and protection.

The Mississippi Flyway, a major migration route for birds, crosses the Lake Superior Basin. The star shows the location of Chicago, IL.

Lake Superior Basin's avian populations also reflect this north-south transition. In the northern portion of the Basin, boreal species such as the great gray owl, spruce grouse and three-toed woodpeckers are most common. Farther south, species typical of deciduous forests are found, such as rose-breasted grosbeak, scarlet tanager, and red-headed woodpecker. Widespread species such as the American crow, black-capped chickadee, and red-tailed hawk are found throughout the basin. A few species common to western ecosystems, such as the yellow-headed blackbird, are also found locally.

Portions of the Lake Superior basin have some of the highest species richness for breeding birds in North America, especially the southern and northwestern shores. Certain forest species appear to be more abundant, widespread, or productive in northern Wisconsin than in other regions.

Approximately 130 to 150 species, including most waterfowl, shorebirds and songbirds breed within the Lake Superior basin during the summer, but over winter elsewhere. Less than 30 species are permanent residents. Most are owls, woodpeckers and grouse.

A few species, such as the snowy owl, northern shrike and redpolls, breed further north and are only winter residents in the basin. Although not on a major flyway, relatively large numbers of migrants pass through on the eastern and western sides of Lake Superior. These migrants also include introduced species such as the rock dove, house sparrow, starling, and Hungarian partridge among others.

Seabirds are good bioindicators of contaminant levels. Herring gulls and other long-lived fish-eating birds show the effects of prolonged exposure to toxic chemicals and help us understand wildlife health. Most colonial waterbirds had nearly disappeared in the early 1900s before the Migratory Bird Convention of 1916 provided some protection from being hunted for their feathers. After they were protected through federal laws, their numbers began to increase in the 1940s, but by the early 1970s herring gull populations had once again decreased. Persistent toxic chemicals such as PCBs, and dioxin, which affected eggshell thickness and embryonic growth and caused other problems, were to blame. Since these chemicals were banned in the 1960's, herring gull populations are recovering in the Great Lakes, but numbers in Lake Superior have shown declines. This could be due to a smaller food base in Lake Superior or that contaminants remaining in the Lake Superior ecosystem and continue to cause problems in certain areas.

Bald eagle eggs effected by DDT.

Populations of bald eagles declined sharply in the 1950s and 1960s as a result of contamination by toxic chemicals that accumulated in the food chain and affected reproductive success of eagles and other carnivores. Along the Lake Superior shoreline, bald eagles were nearly absent through the 1970s, but the population began to increase as the use of DDT was halted and DDE concentrations began to decrease. DDE is a byproduct of DDT. It inhibits the action of the enzyme that is needed to transfer calcium carbonate to the eggshell.

Many of the songbirds in the Basin are neotropical birds that breed in North America and winter in Central or South America. A Minnesota bird survey in 1995 found that 43 percent of the forest birds are neotropical migrants. Use of the basin by neotropical migrants is important because if the Basin's ecosystem is healthy, it should be an area where these migrants can produce young and serve as source populations.

Research on bird find that their populations are changing based on ecosystems changes within the Basin. As expected with changing land use and greater development pressure, species associated with fragmented forest landscapes are increasing such as the American kestrel, yellow-throated vireo, and warbling vireo. Birds associated with human habitation and human-dominated landscapes are also increasing like the Canada goose, wood duck, blue jay, black-capped chickadee, house wren, and eastern bluebird.

Yellow Warbler, a neo-tropical bird that frequents Lake Superior's wetlands.

Four aquatic species, the common loon, pied-billed grebe, double-crested cormorant, and great egret, are increasing. This is likely due to the banning of chlorinated organic toxic chemicals, like DDT, that affected reproduction rates. Numbers of bald eagles and osprey have increased for the same reason

A decreasing amount of farmland and agricultural landscapes have caused species like of upland sandpiper, red-headed woodpecker, northern flicker, field sparrow, vesper sparrow, meadowlark to decline As abandoned fields begin the process of succession and grow up into shrubs and wetlands areas area restored, birds such as the common snipe, sedge wren, LeConte's sparrow, and swamp sparrow are becoming more common.

Conservation of migratory songbirds remains uncertain because of the complex interactions between birds and their landscapes. Lake Superior forests provide very important habitat for migratory songbird populations. With concerns expressed nationwide over the decline of neotropical migrants, the Lake Superior basin should be considered a critical region for migratory songbird conservation. Significant work continues on population monitoring; some of this is being linked to habitat changes.


wood frog
Wood Frog

The Basin's reptiles and amphibians, called "herpetofauna", limited to 17 species of amphibians and 14 species of reptiles, primarily due to the colder northern climate. Reptiles include at least eight species of snake, most of them south of Lake Superior, and five species of turtles, including Blanding's and wood turtles which are declining throughout much of their North American range. The spring peeper, American toad, northern leopard and wood frogs are the most abundant of 11 frogs and toads species, and the eastern newt, eastern redback and blue-spotted salamanders are the most widespread of the seven species in the salamander family.

Populations of amphibians and reptiles are affected by many factors, and the overall trend for any species is not known. As with many vertebrates, the widespread changes in habitat cover across the landscape have had a dramatic effect on the community composition of amphibians and reptiles.

The decline of many amphibians are becoming a concern worldwide.


lake sample
Sampling for microinvertebrates

About 90 percent of the nearly one million species of animals in the world are terrestrial or aquatic invertebrates (animals without backbones). In the Great Lakes region the larger, more easily seen invertebrates include insects and mollusks, such as snails and clams. Insects are the most diverse group and globally may have the largest collective biomass of all terrestrial animals. Yet, within the Lake Superior basin, we have little information on status and trends of the insect or terrestrial invertebrate populations.

Along with an appreciation of the interaction between plants and animals, the role of soil invertebrates, fungi, and microorganisms in ecosystem functioning must be understood. Interdependencies of every part of the biotic community, including the decomposers, are important to healthy ecosystems.



We all live with some degree of stress. As humans we can usually manage our stress levels by changing our habits or moving away from a stressful environment. Plants and animals cannot do this. Environmental stressors are factors that seriously effect plant and animal species to the point of affecting their ability to survive.

Different species react differently to stresses on the environment. What stresses one species, may be beneficial to another. These are significant changes caused by human activities that stress plant and animal communities within the Lake Superior Basin today.

forest line
Fragmentation of a forested area due to new road development can affect species survival.

Forest Management Practices: Because the Lake Superior Basin is primarily forested, the management of its forest habitat strongly affects bird species diversity, abundance, and productivity. Some species have specific habitat requirements that must be met for their survival. For example, American marten and fisher require blocks of mature forest, and marten seem to prefer forests with a coniferous component. Habitat changes and forest management policies affect each species differently. Forests that are managed by removing mature trees before they fall, eliminate habitat needed for species that require litter and downed logs. Clear-cutting, a forest management practice in even-aged or conifer stands, may affect amphibians by changing soil moisture and acidity conditions.

Zebra Mussels

Invasive Species:

The non-native plant, purple loosestrife, invades and dominates wetlands. These wetlands lose many microhabitats that are needed by invertebrates, causing a decrease in invertebrate diversity, which can negatively affect amphibians and reptiles in their aquatic stage.

Human Development and Land Use: Research shows that as development increases, ground-nesting birds decrease in numbers, probably due to vegetation alteration, increased predation, and nest disturbance. Songbirds that nest on or near the ground are also susceptible to predation by domestic cats and dogs.

Habitat fragmentation also causes loss of migration corridors and loss of the mosaic of wetland types that are often critical for amphibian life cycles, especially during drought years. Migration corridors for reptiles are often disrupted by roads and trails, which can directly cause mortality of turtles

Improper shoreline development can destroy habitat and increase runoff and sedimentation.

Shoreline Development: Habitat changes created by shoreline development affect many species of birds and create dramatic changes in bird communities. Insectivorous (insect eating) birds are less common along developed shoreline. The proportion of omnivores, nectivores, frugivores, or seed eaters (birds that favor eating seeds, nectar or just anything such as at a bird feeder) is two times greater at developed lakes than at undeveloped lakes.

Intensive shoreline development also eliminates habitat for certain water-dependent species such as herons and kingfishers. Species like loons can be negatively affected by direct human disturbance. Unsuspecting recreational users sometimes chase birds off their nest, leaving eggs or chicks susceptible to heat or cold. Loons also become entangled in commercial trap nets, fishing lines and hooks, and ingest lead fishing sinkers.

Shoreline development can have serious effects on fish and devastating consequences to amphibian populations. If an adequate natural buffer of vegetation is not left between the developed area and the water's edge, erosion from the land can cause sedimentation of fish spawning areas. Pollutants, like lawn fertilizers and pesticides, can wash into habitat used by fish and amphibians. Down-to-the-shore development also breaks up natural travel corridors amphibians use for feeding, breeding and dispersal. Some turtle species are long-lived and consume animal matter, making them especially susceptible to contamination by toxic pollutants.

Chemical Contaminants: Mammals that are top predators accumulate toxic chemicals in their bodies. These chemicals might be affecting their individual health and reproductive capability. The presence of elevated levels of toxic chemicals coincides with poor health, reproductive impairments, and other physiological problems especially in birds that feed higher in the food chain such as herring gulls, bald eagles, and terns. They cause reduced hatching success, eggshell thinning, abnormal adult behavior, and health problems caused by persistent chemical contaminants. Sources of these contaminants atmospheric deposition, agricultural land run-off, slow leaching of discarded stocks of pesticides and other chemicals from landfill sites and agricultural soils, and contaminated lake/river sediments.

deer railSpecies Overpopulation:



clean upWhat would make up a healthy Lake Superior ecosystem. The Lake Superior Binational Program supports these indicators should be present in a healthy ecosystem.

- All indigenous or native species are present. If they are not present, the habitat exists to rehabilitate or restore species that once existed there.

- Predator and prey interactions are intact and in balance over the long-term.

- Populations fluctuate in natural cycles relative to one another.

- Energy flows naturally from one trophic or food chain level to another.

- No populations are so high (such as white-tailed deer) that they impact other populations in a negative, long-term manner

- There are enough healthy young offspring produced to sustain populations

As with ecosystems, human-caused stresses must be managed to recreate a healthy habitats for plants and wildlife community. People living in and using the Lake Superior basin must understand the value of healthy habitat to a healthy ecosystem.



man on beach CREATE... your own service learning experience to protect and restore aquatic communities. This section provides you with a template to get started in developing your own service learning project.
girl with net ACT... Take action to help restore and sustain aquatic communities and learn about what others are doing in the Lake Superior Basin and your community. This section will give you hands-on things you can do to help!
group reflects REFLECT.... Share and celebrate your experiences with others. This section lets you share what you learned with others.



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