The Battle Against Aquatic Invasive Species

How five invasives are changing our waters, and what you can do to help

Tens of millions of recreators enjoy Michigan’s waters every summer—swimming, boating, fishing, and kayaking in the Great Lakes and the state’s numerous inland rivers, streams, and lakes. But just below the surface, other visitors are present: invasive aquatic species that are profoundly changing our local waterways.

We look at five such species, what’s being done to combat them, and what could be coming next—plus how you can get involved.

Eurasian Watermilfoil

What It Is: Native to Europe, Asia, and North Africa, Eurasian watermilfoil is a feathery aquatic plant that can form thick floating mats in bodies of water. Those mats shade out native plants, impede fish habitat, and obstruct boating and swimming. The plant is tenacious, hybridizing with native plants and spreading easily. Even a small fragment—say, a strand snagged on a propeller—can hitchhike to another body of water and start an entire new colony.

Where It Is: The invasive weed has been a problem across Michigan for decades, according to Michigan State University Extension. In northern Michigan, Eurasian watermilfoil has been found in “Crystal Lake, Duck Lake, Higgins Lake, Houghton Lake, Long Lake, Paradise Lake, Portage Lake, and Walloon Lake, among others,” according to the Lake Leelanau Lake Association (LLLA). That group has partnered with the Grand Traverse Band of Ottawa and Chippewa Indians to combat the plant after it was discovered in Lake Leelanau in 2019.

How It’s Controlled: The LLLA has been able to reduce Eurasian watermilfoil from an estimated 7-10 acres in Lake Leelanau when first found to a handful of locations today, according to Director of Administration and Programs Annalise Povolo. The group uses biodegradable burlap blankets, called benthic barriers, to smother the plant. Still, Eurasian watermilfoil can be difficult to eradicate once established.

“We put a lot of focus on prevention,” says Povolo. “We have a boat washing program with four cleaning stations around Lake Leelanau that are staffed on the busiest days. And we have a community monitoring program where volunteers walk the shoreline and scout for fragments. Stand-up paddleboarding is another great way to spot it.”

The Benzie Conservation District also offers education, monitoring, and boat wash services across northern Michigan. More details are available at LakeLeelanau.org and BenzieCD.org.

New Zealand Mudsnail

What It Is: Brown to black and one-eighth-inch long, the New Zealand mudsnail made its first devastating inland appearance in Michigan in 2015 in the Pere Marquette River. The mudsnail reproduces by cloning, meaning that “a single female could result in a colony of 40 million snails” in one year, according to the Michigan Invasive Species Program (MISP). They blanket river beds and live outside of water for days, making them easy to transport on boats, anchors, and fishing gear.

Where It Is: Populations have since been found in the Au Sable, Boardman, Grass, Pine, and Upper Manistee rivers, according to MISP. “They are most commonly found in our high-value, cold-water trout streams,” says Michigan Aquatic Invasive Species Program Coordinator Cecilia Weibert in the Water Resources Division of the Michigan Department of Environment, Great Lakes, and Energy (EGLE). “Our concern is that it’s occurring in areas where we want to maintain valuable habitat for anglers.”

Heather Smith of The Watershed Center Grand Traverse Bay, which averages 75 volunteers monitoring 25 different stream sites, says a volunteer started seeing tiny snails in Traverse City’s Mitchell Creek in 2023, with sampling confirming New Zealand mudsnail. The Watershed Center and other groups—including MISP, Oakland University, and Trout Unlimited, which are part of the New Zealand Mudsnail Collaborative—now all work to monitor watersheds and educate the public on the mudsnail’s spread. More information is available at NZMSCollaborative.org).

How It’s Controlled: “There aren’t any great control mechanisms when we find them,” says Weibert. “This is one where we’re very reliant on prevention, because we don’t have a good tool that’s also not going to impact our native species.” Anglers are encouraged not to visit multiple rivers on the same day and to avoid felt-soled waders. “Clean, drain, dry is the gold standard,” says Weibert, referring to the slogan for always disinfecting gear and boats before moving between bodies of water.

Didymo

What It Is: Also known as “rock snot,” didymo is a microscopic algae that “produces stalks that form thick mats on hard surfaces like rocks in stream beds,” according to MISP. “It looks and feels like white or tan/brown wet wool.” It can range from small cotton ball-sized patches to thick blankets to long ropes flowing in currents. Like mudsnail, didymo can cover streambeds and reduce habitat for macroinvertebrates, a key food source for fish like trout.

Where It Is: Another invasive that’s often spread by anglers and recreators, didymo has been found in the St. Marys, Upper Manistee, Boardman, Au Sable, Jordan, and Rapid rivers.

How It’s Controlled: No effective tools exist yet for eradicating didymo. Backed by grant funding, Michigan Trout Unlimited is helping lead the charge to “expand monitoring and early detection of this invasive species and better understand the environmental drivers of bloom formation,” according to the group. Residents who are willing to help sample waterways as part of a citizen scientist program can contact the organization through its website (MichiganTU.org).

“Didymo can exist as a regular algae and hang out and be fine, but then suddenly these dramatic blooms will happen,” says Weibert. “With samples, we can analyze the water and try to understand the factors affecting those blooms.”

Quagga Mussels

What It Is: Brought to the U.S. from Eastern Europe through ballast water in the 1980s, the quagga mussel—which has been called the “zebra mussel’s evil cousin because it is much more prolific and can survive from the water’s surface down to 500 feet,” according to the National Park Service—has transformed the Great Lakes. Quadrillions of the filter feeders now blanket the lakebeds, voraciously consuming phytoplankton and algae, triggering a reaction up the food chain that has decimated fish populations, notably whitefish. Their presence has increased the water clarity of the Great Lakes, which may seem like a positive but has the decided down side of meaning few nutrients are in the water.

Where It Is: Quagga mussels are widespread throughout all five Great Lakes. Though rarer inland, infestations have been found in Crooked Lake, Torch Lake, Elk Lake, and Mullet Lake.

How It’s Controlled: The sheer size of the Great Lakes and the difficulty of reaching populations hundreds of feet underwater have made containing quagga mussels an uphill battle.

But there have been bright spots. Good Harbor Bay off Sleeping Bear Dunes and Thunder Bay in Lake Huron are two sites where a variety of local, state, and federal partners have been testing mussel control methods as part of the Great Lakes Spawning Whitefish and Invasive Mussels (SWIM) Project. Experiments range from manual removal to smothering mats to biopesticides. No silver bullet has been found, but the work could produce breakthroughs that help restore key spawning reefs (find out more at GLC.org).

The bipartisan Save the Great Lakes Fish Act, which both the U.S. and Canadian sides of the Great Lakes Fishery Commission (GLFC) have urged Congress to pass, would authorize $50 million annually for 10 years on a coordinated effort to address invasive mussels.

Sea Lamprey

What It Is: Nicknamed the “vampire of the Great Lakes,” the sea lamprey is a parasitic, jawless fish native to the Atlantic Ocean. Resembling an eel, the fish is most famous for its suction-cup mouth full of sharp teeth, which it uses to clamp onto other fish and feed on their body fluids. An individual can kill up to 40 pounds of fish over a 12–18-month period, according to GLFC Policy and Legislative Affairs Director Greg McClinchey.

Compounding matters, the sea lamprey lacks natural predators in the Great Lakes and has a high reproduction rate. “A single female has about 100,000 eggs,” McClinchey says. “They have the ability to get very bad, very fast.”

Where It Is: Sea lampreys are found in all five Great Lakes. While they spend their adult lives in the big lakes, they migrate up rivers and streams to spawn. Larvae can live in the mud for up to 10 years before becoming parasitic juveniles.

How It’s Controlled: Of all the invasives on this list, sea lampreys are up with quagga mussels in terms of having a “profound existential impact” on the Great Lakes, says McClinchey. However, they also have a major vulnerability. Scientists in the 1950s discovered that the lampricide TFM could kill larvae while leaving surrounding organisms unharmed. Before TFM’s discovery, sea lampreys killed more than 100 million pounds of Great Lakes fish annually. That number is now under 10 million, with sea lamprey populations reduced by more than 90 percent.

“We take out about 9 million sea lamprey per year, which is enough to control the species but is probably never going to get us to eradication,” says McClinchey. He cautions that any flagging in lampricide application, as occurred during the pandemic, correlates with an immediate rebound in populations.

To protect the Great Lakes’ $5.1 billion fishery, continued funding and research—as with the experimental FishPass system being built in Traverse City, which will test different lamprey control methods—is vital, according to McClinchey.

The Next Invasives

As much as scientists are focused on controlling existing aquatic invasive species, they’re also warily watching for the next baddie that could invade. Weibert cites marbled crayfish, a self-cloning crayfish often found in the pet trade, as one example.

“One individual getting into a water body could be a huge ecological disaster,” she says.

Another species is hydrilla, an aquatic plant that is “1,000 times worse than milfoil,” says Weibert. “That’s one we’re really concerned about.”

McClinchey adds invasive carp to the list, saying GLFC is “working hard with the Army Corps to try and prevent that from coming up the Mississippi River” through a Chicago-adjacent facility. “This is the last stand,” he says.

MISP has a full list of invasives that are a concern – both those present and not yet occurring in Michigan – with photos and details on how to identify and report them at Michigan.Gov/Invasives.

Prevention Is Key

One key takeaway from the experts is that while new control methods are being tested every day, invasive aquatic species are stubbornly difficult to eliminate once established. That makes prevention the single best weapon in protecting waterways.

Water users are encouraged to do their part, from following the “Clean, Drain, Dry” rule to not releasing any pets into waterways to volunteering with monitoring and clean-up efforts.

“It only takes one bad actor” to introduce a harmful species, says The Watershed Center’s Smith. “We’ll probably never be able to eradicate some of these species. But there are localized efforts that are making a difference. We have to remain optimistic and hopeful. Our water bodies are resilient and ever-changing, but we also have to do our best to protect them.”

Pictured: The New Zeland Mudsnail in a stream. Photo courtesy of the Michigan DNR.

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