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More than 180 non-native species have adopted the Great Lakes ecosystem as home.

One-eighty. And counting.

Many of these non-native species you won’t ever encounter because they have minimal impact on the Great Lakes and remain rare after introduction. A fraction of these animals and plants, however, have spread throughout the Great Lakes, becoming invasive, and they are, by definition, harmful.

Zebra mussels form tight clusters

You may have met a few in the form of sharp little striped shells on the beach that hurt your feet, or seen lakes and ponds taken over by thick mats of feathery aquatic plants. But the unpleasant—and harmful—effects of invasive species go way deeper.

Invasives are the non-native species that have so successfully and aggressively adapted to our local ecosystems that they edge out native species through competition, predation, or habitat alteration. The Great Lakes region supports enormous biodiversity, with more than 1,000 native animal species, yet in some habitats, the natives have nearly been eradicated by invasive species.

Invasive species can also endanger human health, directly or through the ecological changes they cause, and have a large economic impact. One-third of U.S.-registered boats are on the Great lakes; recreational boating is a $16 billion industry per year. Add to that a $7 billion annual sportfishing industry and billions more from tourism. Controlling invasives that have decimated local sport fishes, clogged boat engines and water intake pipes, and fouled waters and shorelines runs into millions of dollars every year. These costs will be ongoing because once an invasive species enters the Great Lakes, we can never completely eradicate it.

A round goby sits in the sand with its fins fanned out

Round gobies gather in large numbers and eat native fishes’ eggs.

Lamprey are snake-like invasive fish with round, suction-cup like mouths that latch on and rasp at their prey with many small, hooked teeth.

A single female sea lamprey can lay 70,000 eggs in a breeding season.

For example, sea lampreys, parasitic fish that were one of the first recorded Great Lakes invaders, have been successfully controlled at about 10 percent of their highest population levels, but only through expensive annual combative measures. To date, sea lampreys are the only invasive species in the Great Lakes that intentional control efforts have significantly reduced.

Invasive species have several common characteristics. First, they show aggressive behaviors that outcompete native species. Round gobies will gather in large numbers and eat native fishes’ eggs. Second, invasive species often reproduce rapidly or over long periods of time. A single female sea lamprey can lay 70,000 eggs in a breeding season. Third, invasive species usually lack natural predators. Zebra and quagga mussels have hard shells that protect them from native fishes, though at least some native species seem to be learning to eat some mussels in their diet. Finally, invasive species can tolerate a wide range of environmental conditions. Round gobies, zebra mussels and quagga mussels all survived in the ballast tanks of oceangoing cargo ships with fluctuating temperatures, oxygen levels and other water-quality parameters. The mussels can even survive several days out of the water.

An orange and white koi fish with black dots

Koi carp from the pet and aquarium trade are released—sometimes by accident, more often intentionally—into Great Lakes waterways.

A large shipping ship releases its ballast water into a lake

Some invasive species enter the Great Lakes by hitching a ride in ballast water tanks.

Invasive species enter the Great Lakes by many routes, all associated with human activities. First, some species, like sea lampreys and alewives, used canals and other manmade diversions to follow swimmable pathways into the lakes. Second, species entered the Great Lakes through maritime shipping by hitching a ride in the ballast water tanks. About 30 percent of invasive species entered the Great Lakes on these ships, but since regulation changes in 2008, no new invasive species have been tied to the shipping industry. Third, the pet and aquarium trade is responsible for goldfish, koi carp, and other hobbyist species being released—sometimes by accident, more often intentionally—into Great Lakes waterways. Once these species are present, they continue to spread when aquatic equipment isn’t properly cleaned. Zebra mussels and Eurasian milfoil, an aquatic plant, have been unintentionally spread to smaller lakes and rivers across the United States.

Three young adults carry a heavy log between them as they assist with habitat restoration at Black Partridge Forest.

What can you do?

Being aware is a start. But it’s also important to take action. You can help stop the spread of invasive species as you enjoy the Great Lakes ecosystem and support efforts to prevent new species from entering the Great Lakes.

If you are a boater, make sure you thoroughly drain your bilge, motor and live well in the same water immediately after use. Also, wash your boat to remove mud, plants and any animals that might be on the hull or propeller. To help avoid spreading invasive species, boats and all other watercraft should follow a clean-drain-dry method before moving between water bodies.

Plants are also important invasive species to be aware of in the Great Lakes. If you have a yard or garden, remove all invasive species (like buckthorn, garlic mustard and decorative grasses or reeds like Miscanthus and Phragmites) and replace them with native species. A wide array of native Illinois plants, from groundcover to grasses, flower to shrubs, are readily available through local nurseries and catalogs. In addition to being beautiful, native plants require less upkeep and conserve water. Also, consider volunteering in a href="gid://shedd/Program/4">Great Lakes Action Days (GLADs) with Shedd to help remove invasive species from forest preserves. Removing invasive plant species is important, and so is providing a place for native wildlife to live.

Despite some successes at managing invasive species, new invasive species could enter at any time. The Great Lakes also face the threat of Asian carp, which have spread up the Mississippi River despite more than $600 million in control efforts since 2004. If you are a fisherman, clean all aquatic equipment and make sure you don’t release live bait. Small bait-sized fishes, like the round gobies, are having profound impacts in the Great Lakes, and size does not predict the potential impact of invasive species. Indeed, some of the most profound changes to the Great Lakes have been caused by small fishes and zooplankton introduced by humans.

And learns as much as you can and share your knowledge with others about this important issue.

At Shedd Aquarium, you can see invasive species like Asian carp, round gobies, sea lampreys and alewives—along with many native fishes they threaten—in the At Home on the Great Lakes gallery.

Sam Bugg; Scott Colborne, Ph.D., Daniel P. Haerther Center for Conservation and Research