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The Spiny Water Flea is a recent Lake Superior invader.

A critical issue for the sustainability of Lake Superior Basin's ecosystem is the invasion of aquatic habitats by non-indigenous species. These are plant and animal species that are not native to the Lake Superior ecosystem. Nonindigenous species are called many names including non-native species, exotic species, aquatic nuisance species (ANS) and aquatic invasive species (AIS).

No matter what you call these alien invaders, they are a growing issue in the Lake Superior Basin. Most have been introduced by human activity, either accidentally or on purpose. Because exotic species are living organisms they have been called "biological pollution" and are to be just as threatening to environmental health as pollution caused by chemical contaminants.





Exotic species are organisms that are foreign or not native to an ecosystem. They become invasive when they become very abundant and spread rapidly.

Invasive species can impact an ecosystem in various ways, but the most general impact is competition for food and space with native species. This competition can lead to significant declines, and in some cases complete removal of a native species populations for the environment. The declines or elimination of native species populations in one trophic level can work like a domino effect causing negative effects on native species in other trophic levels.

AIS have ecological and economic impacts. AIS can upset the natural balance within ecosystems through displacement of native species, reduction in species diversity, destruction of habitat, and degradation of water related recreation.

Since the 1800s, more than 139 nonindigenous aquatic organisms have become established in the Great Lakes, including 25 species of fish. Approximately 10 percent of the nonindigenous species introduced into the Great Lakes can be classified as nuisance species. The AIS that are currently the greatest threat to the integrity of the Lake Superior ecosystem include alewife, Eurasian water milfoil, purple loosestrife, rainbow smelt, round goby, ruffe, sea lamprey and zebra mussel.

As of September 2005, a total of 59 nonindigenous species have been detected in Lake Superior. These include 20 fish, 18 plants, 13 invertebrates, and 8 fish diseases and parasites.

These invaders have seriously altered and disrupted Lake Superior ecosystems. Because they are out of their own natural environments, they not controlled by natural factors that would keep their population numbers under control such as parasites and predators. AIS compete with native species for food, territory and breeding areas and often end up threatening the existence of the native species.

Other impacts of AIS can include loss of fish habitat, shoreline erosion, abnormal increase/decrease in aquatic vegetation, increased industrial costs, a decrease in economic benefit from the commercial/sport fishery, and water recreation, and the costs incurred from the cascading effects of these impacts.

The loss to the economy of the Great Lakes Basin caused by the harm of AIS is estimated to be $5 billion annually.



Most of the aquatic invasive species affecting Lake Superior come from environments thousands of miles away, such as in Europe or Asia. How did could they travel so far, from saline to freshwater environments, past so many obstacles, and make it to Lake Superior. The answer is that we gave them a free ride.

Most AIS "hitch-hiked" their way into Lake Superior via ships traveling from Europe and Asia into the Great Lakes.

lakes mapUntil the 1950's the spread of species was hampered by natural barriers such as the open ocean, different salinity levels, and the inability of organisms to reach hospitable ecosystems on their own. Natural barriers, such as Niagara Falls, stopped the spread of invasives into the upper Great Lakes.

This changed in 1959 when the United States and Canada completed an aggressive engineering project to open the St. Lawrence Seaway that directly connected the Great Lakes to the Atlantic Ocean. The Seaway consists of special locks, canals, and channels along the river St. Lawrence River that allows ships to safely navigate around or through natural barriers that once separated the Lakes from each other and the Atlantic Ocean. Ships could travel from ports in Europe or Asia through all the Great Lakes including Lake Superior. It was a tremendous benefit to international trade for both countries.

While a benefit to local economies based on the shipping, the Seaway also opened a water highway for aquatic invaders. Invasive aquatic species could use to same water highway swim their way into Lake Superior. More often the ocean going ships themselves became the vehicle that brought aquatic invaders into Lake Superior.

Here are some of the ways aquatic nuisance species have invaded Lake Superior:

Dumping ballast waters has been implicated in spreading AIS into Lake Superior.

Ballast Water
All cargo ships contain huge ballast tanks. These tanks are filled in port to help stabilize ships as they travel, and are emptied once cargo is loaded. Each tank can hold millions of gallons of water. When a ship pumps in water to fill its ballast tanks, it also sucks up any and all of the aquatic life found in port waters and sediments. Everything from bacteria and algae to worms and fish has been found in ballast water.

Ocean going vessels from ports in Europe or Asia take on ballast water from their homeport for stability when crossing the Atlantic Ocean for destinations within the Great Lakes. Once in port, the ballast water is not needed anymore and it is pumped out of the ship and into the lake. Whatever organisms are in the ballast water from the ship's homeport have been given a ride half way around the world and are dumped with the ballast water into Lake Superior.

Trans-oceanic ships now are required to exchange ballast water in the open sea at least 200 miles from U.S. coasts under regulations implemented in 1993 by the U.S. Coast Guard. The exchange system requires ships to replace pumpable ballast water at sea with open-ocean water. The idea is that this reduces the number of organisms available for discharge and exposes those remaining to salt water, which may kill them or affect their ability to reproduce. However, ballast exchange may not totally eliminate or affect organisms in the sludge and sediment on the bottom of a ship's ballast tanks.

Ships that claim that they have "no ballast on board" are called "NOBOBs". These vessels are exempt from the mandatory ballast exchange. About 90 percent of the saltwater ships entering the Great Lakes are NOBOB vessels and are not covered by the ballast water. This has been a problem because many exotic organisms still exist in the sludge of ballast tanks of NOBOB ships, and are released into the ballast water when the ballast tanks are refilled.

NOBOB does not mean NO AQUATIC INVASIVES. According to the National Oceanographic and Atmospheric Administration's (NOAA) Aquatic Invasive Species Research Center, a diverse group of phytoplankton and invertebrate eggs and larvae have been found in the residual ballast water and sediments of NOBOB ships, including dozens of non-indigenous species not reported in the Great Lakes. The results of their research confirm that NOBOB vessels are vectors for non-indigenous species introductions to the Great Lakes Basin. New regulations are proposed to close the NOBOB loophole.

Not all of these organisms that hitchhike into Lake Superior's aquatic environment will survive in the Lake Superior environment. There are some that have proven very hardy and adaptable. They have no natural predators in their new environment and multiply quickly. Some invasive organisms can become toxic, posing threats to other species, aquaculture stocks, and humans. Non-native aquatic organisms can also crowd out native species by reducing the food supply or changing characteristics of the habitat.

Examples of AIS introduced by ballast water into Lake Superior include the Eurasian ruffe, round and tubenose goby, spiny waterflea, and Asian clam.

Human Made Structures
Canals that interconnect navigable water such as the Welland Canal was opened in 1833 to bypass Niagara Falls and create a navigable passage between Lake Erie and Lake Ontario for both ships and aquatic invasives. The Welland Canal would later become part of the St. Lawrence Seaway. Approximately 40,000,000 metric tons of cargo is carried through the St. Lawrence Seaway at the Welland Canal annually by over 3,000 ocean and lake vessels.

The Seaway's locks and dams work like steps to allow both transoceanic ships that may be carrying aquatic invasives in their ballast water to move between each of the Great Lakes. It also creates a stairway for AIS to migrate into Lake Superior. Examples of AIS migrating into Lake Superior via the St. Lawrence Seaway include the sea lamprey, white perch, and three-spine stickleback.

boat trailer
Eurasian Watermilfiol is another AIS that can be spread on boating equipment.

Human Transport
Aquatic invaders can hitchhike a ride into Lake Superior on boat hulls, boat trailers, and fishing equipment. Some AIS that have been known to attach themselves to vessels or equipment include the zebra mussel, Eurasian watermilfoil, and the Spiny Waterflea. The Spiny Waterflea has been found in one inland Wisconsin lake with the Lake Superior Basin. Local fisherman, who commonly fish both Lake Superior and this inland lake, are suspected of spreading Spiny

Waterfleas on their boating and fishing equipment. Once introduced to the Great Lakes, nonindigenous species spread inland, frequently by way of barges, recreational watercraft, bait buckets, fish stocking, and other human-assisted transport mechanisms.


Unwanted bait into an ice fishing hole can introduce an exotic species into a lake.

Aquaculture & Bait
AIS can be introduced through the fish farming-bait production industry and the improper disposal of bait. An example of an AIS introduced into Lake Superior from this pathway is the rusty crayfish. It is believed that rusty crayfish were introduced into Lake Superior after some excess crayfish being used for bait were dumped back into the Lake. Rusty crayfish may also have entered the Lake via tributaries connected to inland waters where they were grown by bait dealers.

large carp
Asian Carp are not just ugly, they pose a serious threat to the entire Great Lakes ecosystem.

The common carp was also introduced into Wisconsin for the purpose of aquaculture. The introduction of Asian carp into the Mississippi River Basin occurred accidentally from an aquaculture-based industry. Two species of Asian carp -- the bighead and silver -- were imported by catfish farmers in the 1970's to remove algae and suspended matter out of their ponds. During large floods in the early 1990s, many of the catfish farm ponds overflowed their banks, and the Asian carp were released into local waterways in the Mississippi River Basin.

The carp have steadily made their way northward up the Mississippi, becoming the most abundant species in some areas of the River. They out-compete native fish, and have caused severe hardship to the people who fish there.

The Chicago Sanitary and Ship Canal, which connects the Mississippi River to the Great Lakes via the Illinois River. Recent monitoring shows the carp to be in the Illinois River within 50 miles of Lake Michigan.

An electrical barrier installed in the Illinois canal system is all that separates Asian carp from being introduced into the Great Lakes.

Asian Carp are a significant new AIS threat to the Great Lakes because they are large, extremely prolific, and consume vast amounts of food. They can weigh up to 100 pounds, and can grow to a length of more than four feet. They are well suited to the climate of the Great Lakes region, which is similar to their native Asian habitats.

Researchers expect that Asian carp would disrupt the food chain that supports the native fish of the Great Lakes. Due to their large size, ravenous appetites, and rapid rate of reproduction, these fish could pose a significant risk to the Great Lakes Ecosystem. Eventually, they could become a dominant species in the Great Lakes.



Investigate more about Lake Superior's invasive and native fish species.

Alewife is a fish closely related to the Atlantic herring. It invaded Great Lakes around 1953 after the building of the canal systems and got to Lake Superior in 1954. Alewives prey upon the larvae of native fish species. Although they were not as much of a problem in Lake Superior as the other Great Lakes, they were once a serious threat to native fish and recreation, until another non-native salmon species were introduced as a biological control. The salmon proved to be a well like recreational fish species, too.

However, there is still a problem. Alewives have a high concentration of the enzyme thiaminase, which causes mortality of newly-hatched salmon larvae.

eurasian watermilfoilEurasian Watermilfoil
Eurasian watermilfoil is like aquatic quackgrass. It forms masses of vegetation in nutrient-rich lakes (usually inland). It crowds out native aquatic vegetation and interferes with water recreation. It is unclear at this point how much of a threat the Eurasian Watermilfoil poses to the Lake Superior ecosystem.

Purple Loosestrife

purple loosestrife plantPurple loosestrife (Lythrum salicaria) is a plant native to Europe that was first brought to North America in the early 1800s. Purple loosestrife is now found growing as dense stands of invasive plants growing wetlands and coastal areas throughout much of the United States and Canada. It invades wetland areas and has a competitive advantage over native plant species due to its ability to spread by roots and produce over 2 million seeds per plant annually. It creates a habitat that is unsuitable for native wetland animals. Control measures used on purple loosestrife include physical removal, chemical treatment, and biological control through introduction of natural predators, European beetles and weevils.

rainbow smeltRainbow Smelt
Rainbow smelt (Osmerus mordax), native to the Atlantic coast, entered Lake Superior around 1930. Rainbow smelt populations grew rapidly during the 1950s and 1960s, and became the dominant prey species for lake trout in Lake Superior. Rainbow smelt became the principal forage fish for lake trout and other top predators and have been implicated as a competitor for the native lake herring, whose populations collapsed during the buildup of the smelt population. The rainbow smelt population continued to grow until the late 1970s and then declined greatly due to heavy predation by trout and salmon, reaching all-time low levels of abundance in the early 1980s. Rainbow smelt prey upon the larvae of native fish and eat a diet that broadly overlaps that of other native cisco species. Smelt are the preferred food for predator fish, and have profoundly changed the flow of energy through the Lake Superior fish community. Rainbow smelt also contain thiaminase (about half as much as alewives) and therefore have a negative impact on the survival rate of newly hatched salmon. Fishery management agencies in the Lake Superior Basin have agreed that rainbow smelt is an undesirable species that should not be protected from fishing.


round goby
Round Goby, Seagrant photo

Round Goby
The round goby (Neogobius melanostomus) is a small, bottom-dwelling, soft-bodied fish. It is native to the Black and Caspian Seas. The round goby was discovered in Lake Superior in the St. Louis River Estuary at the Duluth-Superior harbor in 1995. It is believed that round gobies were introduced to the Great Lakes through ballast water transfer. The goby is currently poised to enter almost half the United States through connected waterways unless its progress can be halted. The round goby is currently found 44 miles downstream in the Illinois Waterway, which connects to the Mississippi River.

Round gobies are particularly threatening because they are aggressive, territorial, and competitive for food, spawning, and shelter areas. They are highly tolerant of a variety of environmental conditions that most native species cannot exist in. They feed on eggs and fry of native fish and have a large body size compared to similar bottom-dwelling fish species.

On the positive side, gobies eat large quantities of small zebra mussels, up to 78 mussels per day in laboratory settings. Because gobies eat zebra mussels and in turn are eaten by other fishes. Contaminant transfer from zebra mussels to the goby and onto to highly valued fish species is an issue. Research is underway to investigate the severity of this problem.


The ruffe (Gymnocephalus cernuus), a small perch-like Eurasian fish, was first detected in the estuary of the St. Louis River and Duluth-Superior harbor area in western Lake Superior in 1986. It became very abundant in the favorable habitat of the nearshore waters, raising concerns about competition with native species. It is believed to have been transported there in the ballast water of seagoing vessels. By 1991, the ruffe was the most abundant species in the St. Louis River estuary. The Great Lakes Fishery Commission estimates the European ruffe could cause annual losses of $105 million annually if not controlled. A control program for ruffe was approved in 1995 and has been successful in delaying the spread of ruffe in the Great Lakes and inland waters. Like many exotics, ruffe are prolific breeders, yet they do not have any natural predators in their new environment to keep their populations numbers under control. They also can survive in a wider range water temperatures and water quality than native species. Ruffe have become very abundant in this favorable habitat, raising concerns about its competition with native species.

sea lampreySea Lamprey
The sea lamprey (Petromyzon marinus) is an eel-like, jawless fish that attaches itself to the body of a fish and sucks blood and tissue from the wound. The lamprey is native to coastal regions on both sides of the Atlantic and was first noticed in Lake Ontario in the 1830s. Originally, Niagara Falls served as a natural barrier to keep sea lampreys out of the upper Great Lakes. However, when the Welland Canal was constructed in 1829 for the shipping industry, a new route for sea lampreys was opened and the invasion of the upper Great Lakes began.

In 1921 the lamprey was discovered in Lake Erie, in 1936 in Lake Michigan, in 1937 in Lake Huron and finally in Lake Superior in 1938. The sea lamprey is considered the most devastating of all AIS to have infested the Great Lakes. An explosion in the sea lamprey population caused extinction in lake trout in all the Great Lakes except Lake Superior. It is only through control and restocking activities that lake trout populations have recovered. Even today, the Fishery Commission has declared that more fish are taken by sea lamprey every year than by commercial and sport fishing combined. An international control program under the Great Lakes Fishery Commission has successfully suppressed sea lamprey populations since about 1960. This control program is the oldest control program in existence in the U.S., and yet all efforts have still been unable to eradicate the species from the Great Lakes ecosystem.

zebra mussel
A water pipe clogged with zebra mussels.

Zebra Mussel

The zebra mussel (Dreissena polymorpha) is native to the Caspian Sea region and quickly spread throughout Europe before the Industrial Revolution. It is believed to have entered the Great Lakes region in 1985 or 1986 through ballast water discharge. By 1989, zebra mussels could be found in all of the Great Lakes, as well as many inland lakes. Under the right conditions, zebra mussels reproduce quickly, are very prolific, and are very tolerant to a wide range of environmental conditions. Environmental conditions in the Lake Superior basin have generally prevented reproduction by zebra mussels, though mild weather in recent years has apparently allowed reproduction to occur in the St. Louis Estuary.

Zebra mussels compete with native species for phytoplankton and zooplankton, are believed to contribute to the cycling of some contaminants, fundamentally alter the habitat and food webs, and are harmful toward native mussels to the extent that they kill native mussels by encrusting their shell so heavily that the native species cannot open to feed or breathe.

Beyond their ecological effects, zebra mussels also create serious financial costs for facilities that draw water from the Great Lakes by clogging water intake systems. Although various methods are being explored, no effective means of control in natural aquatic systems has yet been found for zebra mussels in the Great Lakes.


terrestrial invader plant

There are other terrestrial nuisance species threatening the biodiversity of the Lake Superior Basin. Terrestial invasive species are generally easier to control than aquatic invaders because they are easier to see and access because they are land based.

Investigate more about terrestrial and aquatic invasives.



controlling invasive plants
Controlling Purple Loosestrife with Galerucella, a predatory beetle.

Eradication of existing aquatic invasive species in the Lake Superior Basin is currently not feasible. Populations of some aquatic invaders, like Purple Loosestrife and Sea Lamprey, can be controlled to reduce their impacts on the ecosystem to a level that is tolerable for the sustainability of native species. However it is very expensive and time consuming.

Early detection of the presence of new AIS or the spread of an invader followed by rapid response is the preferred course of action for AIS control. Early detection requires environmental surveillance/monitoring activities. Rapid response can consist of removal/reduction activities, public education, regulations to stop the spread, collaboration between government and tribal agencies, and research.

The most effective way to control AIS is to prevent the introduction of new AIS, and prevent the spread of existing AIS.

ANS can be controlled by several general methods, including chemical, biological, mechanical or physical, and habitat management practices. While each of these methods may provide effective control, each has disadvantages as well. The use of chemicals raises concerns about environmental safety and long-term impacts. Identification and screening of biological control agents invariably takes many years, and improperly screened biological control agents have themselves become nuisance species in the past. Mechanical or physical controls are often very expensive. No single method is likely to provide the necessary control of nonindigenous species. Hence, a comprehensive control strategy involving a combination of techniques is often necessary for an effective control program.

Safe, selective, efficient methods are needed to control aquatic invaders.

The prevention and control of ANS has global implications that require policies and programs at various levels of government.



You can help stop the spread of aquatic invasive species by following these guidelines:

Investigate what you can do to help stop the spread of aquatic invaders.


Boatingcleaning boat
When transporting a boat, remove all traces of mud, weeds, animals and organisms from both the boat and trailer

Dump out all water at the boat landing away from the waters edge, including water from live wells, bait buckets, and recreational equipment

Clean and dry everything that came into contact with the water including the boat, fishing equipment, etc. If you have access to a power washer, wash boat, motor and trailer. If possible, allow equipment to dry for 5 days before taking it to another water body.

aquarium snail
The Chinese Mystery or Apple Snail may have been introduced into lakes by water dumped from aquariums.

Aquarium and Aquatic Pets
Do not release or put plants, fish or animals into a body of water unless they came out of that body of water.

Do not dump plants, fish or animals down storm drains either, because most storm drains lead to water bodies or wetlands. This is an important prevention step because many plants and animals can survive even when they appear to be dead. The two categories below describe some common situations where people may feel compelled to release aquatic plants or animals.

If your family gets tired of its aquarium or aquatic pets, do not release anything from the aquarium (water, plants, fish or animals) into or near a body of water or storm drain. Explain to your family or friends how you could be hurting all of the streams and lakes around the country and killing other fish and animals that already live in the water.

If you cannot find a home for the critters in you aquarium, bury them. Dump the water into the toilet or yard, far away from storm drains.

Whether you have obtained bait at a store or from another body of water, do not release unused bait into the waters you are fishing. If you do not plan to use the bait in the future, dump the bait in a trashcan or on the land, far enough away from the water that it cannot impact this resource. Also, be aware of any bait regulations, because in some waters, it is illegal to use live bait.



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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