Learn more about how you can protect the Great Lakes

Aquatic invasive species threaten the fundamental structures and functions of freshwater ecosystems. Water-based recreationists, particularly anglers, can transfer invasive species when equipment used in an invaded waterbody is then used elsewhere. Because invasive species often “hitchhike” on fishing and boating equipment—unbeknownst to the owners—individuals can minimize their spread by taking precautions such as draining water from their boats, removing organic matter from trailers and fishing lines, and properly disposing of unused bait. Once these organisms are present, mitigating their impact is difficult, if not impossible.

Examples of Aquatic Invasive Species

An invasive species is an organism that arrives from another part of the world and establishes a new population outside of its native range. The arrival of an invasive species disturbs the stability and make-up of the new ecosystem, which can reduce biodiversity, degrade habitat for native species, and lower water quality. All of these changes carry important implications for recreational opportunities, ecosystems, and economies around the world, especially in the Great Lakes basin.

Sea Lampreys

Sea lampreys are a type of primitive, jawless fish that parasitize other fish. They feed by suctioning onto prey and using their rows of sharp teeth to bore through skin and muscle. Although there are a few native lamprey species in the Great Lakes, the invasive sea lamprey is the largest and most aggressive. Sea lampreys spread to Lake Erie from the Atlantic Ocean in the 1800s, after humans had built canals and locks connecting the Great Lakes. By the mid-1900s, lampreys had colonized all five lakes. Over time, lamprey abundance skyrocketed, putting intense pressure on a number of native fish species. Lake trout, whitefish, and chub populations saw severe reductions, and fisheries for these species suffered tremendously. Through programs spearheaded by organizations in the U.S. and Canada, sea lamprey abundance has dropped dramatically, but ongoing efforts are required to control their populations and prevent their proliferation.

Left: Sea Lamprey mouth, Credit: T. Lawrence, Great Lakes Fishery Comission (GLFC). Right: Sea Lamprey, Credit: Will Meinderts/Minden Pictures.

Quagga and Zebra Mussels

Zebra mussels were first observed in Lake St. Clair in 1986, and Quagga mussels appeared just three years later in Lake Erie. Despite being newcomers to the Great Lakes, these two tenacious invertebrates have spread aggressively through the lake system. Zebra and quagga mussels crowd out native invertebrates and are ravenous plankton-consumers. Their eating habits can cause dramatic changes to the ecosystem, providing ideal conditions for algal blooms and botulism-causing bacteria. As a result, the tourism industry, fisheries, and wildlife populations of the Great Lakes have seen considerable setbacks. Zebra and quagga mussels also attach to a number of hard surfaces, such as industrial pipes, and removal can be very costly.

Left: Zebra Mussels, Credit: Dave Britton/Invading Species Awareness Program. Middle: Quagga Mussels attached to boat equipment, Credit: Statesman Journal. Right: Zebra and Quagga Mussels, Credit: Division of Boating and Waterways

Round Gobies

Originally from the Black and Caspian Seas, round gobies were transported to the Great Lakes through ballast water. After their first appearance in 1990, they spread quickly to other lakes. Gobies compete with native species, especially sculpins, for habitat, and they even consume other species’ eggs and offspring. It has been observed, however, that round gobies are efficient predators of zebra mussels, and their presence can help control the mussel population. The best way to prevent the spread of gobies to new habitats is taking precautions such as draining livewells and bilges and properly disposing of unused bait.

Left: Round Goby, Credit: David Jude. Right: Round Goby, Credit: Gregory A.D.

Spiny Water Fleas

Spiny water fleas, despite the misnomer, are not insects: they are a type of zooplankton about three-eighths of an inch long. They were discovered in Lake Ontario in 1982 after having travelled from Northern Europe in the ballast water of ships. By hitching a ride on fishing and boating equipment (such as anchor ropes, fishing lines, and bilge water), they have spread throughout the Lakes. They feed on other species of zooplankton and have contributed to the local elimination of native zooplankton species in some areas. Because zooplankton serve as a foundation of the food web, many fish species have suffered as the result of competition with spiny water fleas. In addition, rather than becoming a source of food themselves, their sharp spines make them difficult for most small fish to swallow. There is currently no way to control spiny water fleas, so it is recommended that anglers and boaters drain, wash, and dry their equipment to prevent spreading them to other bodies of water.

Left: Spiny Water Fleas attached to fishing line, Credit: Vermont Department of Fish and Wildlife. Middle: Spiny Water Flea, Credit: Michigan State University. Right: Fishing line with Spiny Water Fleas, Credit: Minnesota DNR


Eurasian Watermilfoil

Having reached North America in the mid-1900s, Eurasian watermilfoil found the nutrient-rich waters of the Great Lakes to be accommodating, and it spread rapidly. Waters infested with Eurasian milfoil have lower numbers of native plants and are often closed for boating and swimming. Milfoil tends to spread to new waterbodies by clinging to boat propellers, rudders, trailers, and other watercraft.

Left: Eurasian Watermilfoil, Credit: Barry Rice, sarracenia.com. Right: Lake infested with Eurasian Watermilfoil, Credit: Ontario Rivers Alliance

Non-Native Cattail

Narrow-leaved Cattail was introduced to the Lakes in the late 1880s, and it hybridized with native species to generate a new species of cattail. Towering above the native vegetation, the non-native cattail species cast shade and on other plants, making it nearly impossible for them to compete. Consequently, native plant biodiversity has dropped dramatically in areas where non-native cattails thrive. Like most invasive species, these cattails are very difficult to control once established.


Left: Narrow-leaved Cattail, Credit: frenchhillpond.org. Right: Pond invaded by Narrow-leaved Cattail, Credit: Mandy Tu, The Nature Conservancy


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