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More than any of the other Great Lakes, Lake Superior's aquatic communities most closely resemble the original community of the Lake prior to European settlement. However, even Lake Superior's aquatic communities are affected by significant human-caused stresses that threaten to reduce its diversity and proper functioning.

Click here for a more complete description of what makes Lake Superior's aquatic habitats unique.


Learning Objectives

Understand the five basic types of fish habitat and species found in Lake Superior

Understand what is being done to stop aquatic habitat loss and sustain fish populations



holding fishThere are five basic fish habitats recognized in Lake Superior, each with a specific array of fish species. The fish community of each habitat type is fairly unique.

Who's Who of Lake Superior Fish? Click on the the fish picture to find out.


Offshore Habitat

This is the open water portion of Lake Superior deeper than 262 feet or 80 meters. It makes up over 75 percent of the total area of the Lake. It is the largest aquatic habitat.

The fish community of the offshore habitat is relatively simple and composed of adult lake trout, siscowets, humpers, burbot, Pacific salmon, sea lamprey, deepwater ciscoes, lake herring, and deepwater sculpins. Siscowets and humpers are actually different forms of lake trout that are found only in Lake Superior. The offshore area is critical habitat for siscowets, humpers, chubs, and deepwater sculpin.

Nearshore Habitat

This is the open water portion of Lake Superior less than 262 feet or 80 meters deep. Most of the important and critical habitat for lean lake trout, lake herring, and lake whitefish is found in the nearshore habitat. The nearshore habitat has a greater number of fish species than the offshore habitat. Some of the offshore species can also be found in this habitat. The fish community of the nearshore habitat is composed mainly of lean lake trout, siscowets, burbot, Pacific salmon, lake herring, lake whitefish, round whitefish, rainbow smelt, ninespine sticklebacks, trout-perch, pigmy whitefish, and longnose and white suckers.

Embayments or "Bays"

aerial shoreline view
The Bark River Estuary is an example of an embayment estuary

These are the nearshore areas that are connected to Lake Superior, but have unique physical properties different because they are partially protected from the physical dynamics that occur in Lake Superior. Embayments can be natural or man-made and include coastal wetlands, bays, harbors, and freshwater estuaries that are subject to lake seiche.

Fish communities living in the embayment habitat are more complex than in the offshore and nearshore habitats because Lake Superior's bays are warmer, more productive, and more physically diverse than the remainder of the Lake. Fish living in the embayments include many of the same fish that live in the nearshore habitat, but also warm and cool water fish species such as walleye, smallmouth bass, yellow perch, rock bass, northern pike, lake sturgeon, johnny darters, emerald shiners, longnose dace, sand shiners, bullheads, and carp.

A tributary river as it flows in Lake Superior

Tributary Habitat

This aquatic habitat includes all rivers and streams in the watershed that empty into Lake Superior. Tributaries are not subject to the seiche effect.

There are over 2050 miles of tributaries available to Lake Superior fish. Many fish that live in the embayment, nearshore, and offshore habitat types spend part of their life in tributaries, but the fish community of tributaries includes brook trout, burbot, lake sturgeon, longnose and white suckers, redhorse suckers, Pacific salmon juveniles, mottled sculpin, bullheads, the many species of minnows, and sea lamprey. Tributaries are the critical habitat for nearly all of these species. Rainbow trout and brook trout are found in more tributaries of Lake Superior than the other major fish species, while lake trout and lake whitefish are found in the fewest number of tributaries.

Inland Lake Habitat

stream and waterfallThere are many inland lakes within the Lake Superior basin that exhibit a wide range of habitat conditions and contain a variety of fish communities. Habitats in these lakes vary from small, shallow lakes to deep, cold-water lakes. The fish species found in inland lakes varies from warm water to cold-water fish communities. The morphology and water chemistry of the inland lakes are dictated by the geology of the Lake Superior basin that includes Canadian Shield, sandstone, and sandy-loam shoals. Lake Nipigon is the largest of the inland lakes within the Lake Superior Basin and is a significant source of the water that flows into Lake Superior.


What's Stressing Out Lake Superior's Aquatic Habitats?

The good news is that most of Lake Superior's nearshore and offshore aquatic habitats have remained relatively unchanged. There is sufficient quantity and quality of these habitats to sustain their fish communities. The bad news is the vast majority of the embayment, tributary, and inland lake habitat has borne the brunt of habitat destruction.

Two environmental stressors impacting all of the Lake's aquatic habitats are atmospheric deposition of critical pollutants and exotic species.

Offshore Habitats can be impaired by Atmospheric deposition, dumping or discharges from ships, and introduction of exotic species habitats despite their deeper water.

Nearshore Habitats are closer to human activities and is susceptible to degradation from industrial pollution, over-exploitation such as over fishing, and mining runoff

Embayments, like the nearshore habitat, tend to be more developed because they are more sheltered environments. Harbors and marine docking facilities tend to be located here. Threats to this habitat type include petroleum emissions and spills, industrial pollution dumping or discharges from vessels, exotic species, over-exploitation, loss of wetlands due to dredging or draining, land-use practices, urban development, sedimentation, and shoreline development.

Besides the tributaries to Lake Superior, a substantial amount of habitat destruction has taken place in the embayment habitat. Most of the Areas of Concern on Lake Superior are located in embayments, particularly in Canada.

Tributaries are susceptible to pollution from industrial effluents that are dumped into them, hydroelectric facilities, barrier dams, loss of wetlands, land-use practices, impacts from timber harvesting, mining, agricultural practices, urban development, and sedimentation. Some tributaries have small coastal freshwater estuaries, which provide habitat for fish and wildlife species.

Most tributaries were impacted by a complete forest cutover in the middle 1800s, extensive fires that followed, and years of watershed damage caused by human land use such as agriculture. Damage to the land created higher peak flood flows and erosion which increased the rate of flow. Woody cover along the rivers was moved. Stream banks eroded and natural channels were changed as a result. Even the rivers' bottom substrates where changed. Although watershed health has generally improved, the channel damage caused during this time period is still not healed. Management actions include land acquisition, beaver control, stream habitat improvement in critical areas, and fishery regulations.

Inland lakes make up some of the pristine aquatic environments in the watershed including portions of the Boundary Waters Canoe Area and are protected against further development.

Demand for other inland lakeshore property continues to increase and threatens lake habitat. Contamination from improperly constructed or maintained septic systems can pollute inland lakeshore areas. Like other shallow water habitats, inland lake habitats can be impacted by sedimentation and run-off from timber harvesting, urban development, and agricultural practices. Many inland lakes also include wetlands, which can also be lost or compromised by these factors

BW photo overfishing
Like many of Lake Superior's vast natural resources, the fishery was thought to be inexhaustible.

Impacts on Fish Communities

Unregulated fishing is partly responsible for the demise of deepwater ciscoes, brook trout lake sturgeon, walleye, lake trout, and lake herring in Lake Superior from the late 1800s to the mid 1900s. Overfishing is currently not as much of a problem on Lake Superior and occurs only in isolated areas on a few fish species, such as lake trout in Whitefish Bay and eastern Ontario waters. Overfishing is currently being prevented through fishery management regulations developed separately or jointly by state, provincial, and tribal agencies.



river full of logs
Lake Superior tributary rivers were dammed to create an efficient way to float white pine logs to mills for processing.

Hydroelectric Development and Dams
The late-1800's to the mid-1900's was also about same time period that hydroelectric development and man-made barriers were placed in Lake Superior tributaries. Dams alter the flow of tributary rivers with impact on fish populations. A few lakes within the Basin are water storage reservoirs used for hydroelectric power. Lake level fluctuations caused by water drawdowns for hydropower generation can negatively affect fish habitat and populations.

Many man-made barriers on Lake Superior tributaries were created during the white pine logging era. They were to hold back water to flush pine logs downstream. Damming the tributaries affected the fish communities by significantly changing the physical properties of the rivers. The logs that were flushed downstream acted like bulldozers as they crashed it the stream banks, the physical destruction of stream channels contributed to the demise of brook trout, walleye, lake sturgeon, and lake trout. Sedimentation of soil eroding off the land due to poor logging and other land use practices clogged tributaries.

Logging, road crossings, beaver dams, and man-made dams are currently causing loss of spawning and nursery habitat in tributaries due to sedimentation and unfavorable changes in the thermal habitat. Walleye populations in Lake Superior are affected by high mercury levels, paper mill effluent, and habitat loss.

Re-licensing of hydroelectric facilities on U.S. tributaries through the Federal Energy Regulatory Commission has resulted in changing waterpower management from peak operations to "run-of-the-river" flows, which are friendlier to aquatic life and fish reproduction.

exotic species fish
Investigate more about exotic species and their impact on Lake Superior.


Exotic Species
Exotic aquatic species are organisms that have either been accidentally or purposely introduced into Lake Superior. Because they are not native to the Lake Superior ecosystem, most do not have a natural predator to keep their population numbers in check. Often exotic species do not serve as a food source for other species, but compete with native species for food and cover.


sea lamprey
The Sea Lamprey is adapted to attach to a fish and suck out its body fluids

Sea Lamprey
This parasitic fish is native to the North Atlantic Ocean and many of its tributaries. Niagara Falls had served as an effective natural barrier to Sea

Lamprey until 1829 when the Welland Canal was constructed to by-pass the Falls to improve access to the Great Lakes for the shipping industry. While the canal may have made shipping easier and more economical, it also opened a direct passage for the Sea Lamprey into Lake Superior. Sea lamprey invaded the lower Great Lakes in the late 1800's and early 1900's and eventually reached the upper Great Lakes in the mid to late 1930's. This exotic species contributed to the collapse of lake trout and whitefish populations from the 1940s through the 1960s. These fish species have not yet fully recovered.

Sea lamprey populations have been successfully suppressed throughout most of Lake Superior because of integrated control using chemicals, barrier dams, and sterile-male releases. It is an on-going control problem that will require active management.

The use of chemicals and barrier dams to control sea lamprey, although good at protecting lake trout and whitefish, present a difficult balancing act to managers because these control tools also have potential negative effects on lake sturgeon migration up tributaries and survival of recently hatched lake sturgeon in tributaries. Sea lamprey continue to kill a substantial number of lake trout in Lake Superior every year.


rainbow smelt fishRainbow smelt
This invasive fish was introduced into the Great Lakes as baitfish. It has provided valuable commercial and sport fisheries on Lake Superior since the 1930s, and has been the primary food source for many of the predatory fish in Lake Superior. When rainbow smelt entered, indigenous fish such as lake herring and whitefish initially decline in abundance, although there has been no direct measure of the effect of smelt on these fish species in Lake Superior. Today rainbow smelt have expanded their range beyond the Great Lakes Basin.


eurasian ruffleEurasian Ruffe
A native of Europe, this perch-like exotic fish was brought into Lake Superior in ballast water ejected from ocean going ships entering Lake Superior's harbors. Ruffe are prolific breeders and can adapt to variety of aquatic environments, and out compete native fish for food.



spiny water fleaSpiny Water Flea
The spiny water flea (Bythotrephes cederstroemi, or "B.C.") is not an insect, but a tiny crustacean with a long, sharp, barbed tail. It is very abundant in early summer in Lake Superior. Like the Ruffe, this exotic hitchhiked its way into Lake Superior in the ballast water of ocean going ships entering harbors like Duluth, MN.

No one is really sure what effect spiny water fleas will have on the ecosystems of the Great Lakes region. But resource managers are worried, because the animals may compete directly with young perch and other small fish for food, such as "Daphnia" zooplankton. Their spiny bodies make them an unattractive source of food for many fish, although some do eat Bythotrephes and this may be a source of control. Spiny Water Fleas have been transported from Lake Superior in other inland lakes within the Basin.


Pacific Salmon
pacific salmonHere's an example of an exotic species has proven to be a valuable sport fish with some commercial fisheries benefit, too. Unfortunately, they may also negatively interact with indigenous brook trout in some tributaries.

Three species of Pacific salmon have been introduced to Lake Superior in the past few decades. All feed in the big lake until they reach sexual maturity. Then, in the fall, they swim up rivers to spawn and then, inevitably, die. The largest, which has fared the best in its new environment, is the chinook salmon (also called king salmon). This fish grows to over 30 pounds, though most catches are around 10 to 15 pounds. Coho salmon, also called silver salmon, are smaller, averaging only about 3 to 4 pounds. The smallest salmon is the pink, or humpy salmon referring to the large hump on the back that males develop during breeding season. These latter two species are much less common in Minnesota waters of Lake Superior than the chinook.

Making changes to the stocking rates of hatchery-reared Pacific salmon typically causes big political problems for fishery agencies because they are now a highly prized sport fish. Since most Pacific salmon now living in Lake Superior are the product of natural reproduction, there are few options available for managing their populations. They are called a "naturalized" species rather than an "exotic".


chemical factoryChemical Contaminants
Other stresses to the aquatic community of Lake Superior are much less easy to recognize or manage. Some of the chemicals being deposited in Lake Superior through atmospheric deposition originate outside of the Lake Superior basin, and even outside North America, making it impossible to address management of them except through international agreements. Chemical contaminants found in the meat of Lake Superior fish do not seem to have limited their ability to reproduce. However, it is not certain if their reproduction rates would be better if the chemical contaminants were in lower concentrations or not there at all.

The presence of chlordane in siscowet trout from Lake Superior is an example of a chemical that originates outside the Lake Superior Basin, yet it is in sufficient quantity in siscowets that consumption advisories have been issued by the state of Michigan. Michigan closed its state-licensed commercial fishery for siscowets in the early 1990s due to chlordane contamination of the fish.


loggingLogging, Mining

Present day logging practices can be regulated to protect aquatic life. These practices are much less stressful to aquatic life than historic methods. The timber industry is implementing best management practices or "BMPs" which specify increased protection of the riparian zone along streams, lakes, and wetlands. Road development, whether by logging companies or municipalities, can have significant impact on the amount of erosion entering streams and affecting fish habitat.

If Best Management Practices (BMP's) are followed, culvert failure and the erosion it causes can be prevented.

Iron ore mining is an important industry in northeast Minnesota and progress has been made to improve water quality near mining sites, but there are still areas that need attention.


Shoreline Development

With the renewed interest in experiencing "wilderness" and the changing demographics of our society there is a major land development boom in the Lake Superior watershed that includes expansion of roads, businesses, cabins/homes, and general shoreline development. These areas are extremely important for both recreation and tourism and the sustainability of some communities.

shoreline development
The loss of shoreline habitat, due to improper development practices, threaten water quality and fish habitat.

Shoreline development has resulted in a reduction of aquatic habitat and in some cases a reduction in water quality due to runoff and erosion. This may affect the survival and reproduction of some fish species, such as yellow perch and northern pike. Land use practices and urban development alter drainage patterns and increase surface water run-off, but the effects on the aquatic community are difficult to assess and understand.

Management actions to improve water quality include acquisition of remaining undeveloped shoreline near fish spawning areas and wildlife marshes, and improvement in sewage treatment facilities.



Overexploitation of Fish
The early history of the Lake Superior fishery was one of overharvest. Lake Superior's native stock of lake trout almost went extinct from overfishing combined with sea lamprey predation. Today, sport and commercial fishing regulations are carefully monitored by federal, state, and tribal natural resource agencies.

General mercury advisories for fish consumption exist recommending that smaller and leaner fish should be eaten. Specific advisories exist for some inland lakes for mercury as well as PCB contamination.



One of the issues for the Lake Superior's aquatic communities is a just lack of good quality information about them and the stresses that are impacting them. Restoration of the Lake Superior ecosystem can only occur once we understand the linkages between habitat and the aquatic community structure and function. The lack of information is as much a problem to restoring the health of the aquatic community as the actual destruction that has been caused on the ecosystem. Here are four priorities that will lead to finding solutions to sustaining Lake Superior's aquatic communities and how to discover some of the successes that are being achieved:

Monitoring Fish Communities: There is a need for a standardized lakewide monitoring program to evaluate the status of Lake Superior's fish communities in deep water, nearshore, embayment, and tributary environments. Investigate more about monitoring successes at:

thin silve fishRestoring Critical Habitat and Native Fish Populations:

sharkInvestigate more about sturgeon restoration in the Great Lakes and Lake Superior.

A related priority is to determine the current population status and abundance of lake sturgeon in historic spawning streams and to quantify sturgeon-spawning habitat in those streams. Lake sturgeon were historically very abundant in the nearshore and tributary habitats of Lake Superior, but a combination of habitat destruction, hydroelectric development, and over-fishing resulted in the lakewide collapse of the populations early in the twentieth century. The current lake sturgeon rehabilitation plan gives this work high priority for future research.

Controlling Invasive Species: One of the greatest threats to restoring native aquatic species is controlling aquatic invasive species that threaten the sustainability of their population. Investigate efforts to control Lake Superior's aquatic invasives at:



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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