DULUTH, Minn. — The news at times seems all bad when it comes to aquatic invasive species in the Northland.
Every year more lakes are infested with zebra mussels, starry stonewort, spiny water fleas, Eurasian water milfoil and more. Asian carp are moving up the Mississippi River system, and snakehead fish — that breathe out of water and can move on land — aren’t far away.
Aquatic invasive species, or AIS, have saturated some of our most popular waters, like Mille Lacs, Winnibigoshish, Lake of the Woods and the St. Louis River estuary. It seems just about every lake and river now has some sort of invader. And it seems inevitable that even the lakes that don’t have them will get them soon.
Only that’s not the case at all.
In Minnesota, only 8% of all lakes have a verified aquatic invasive species. And officials say the math shows that efforts to slow the spread of AIS are in fact working. “Stop Aquatic Hitchhikers” and “clean, drain, dry and dispose” have become ingrained on many Northlanders' boating checklists, like life jackets, minnows and sunscreen.
“What we’ve learned is that it’s not inevitable that every lake is going to get them. That’s not what’s happening,” said Doug Jensen, the Duluth-based aquatic invasive species expert for Minnesota Sea Grant, who helped develop public outreach campaigns for AIS over the past 20 years. “And the numbers show that the spread is much, much slower than if we had done nothing at all.”
Zebra mussels have now been confirmed in 214 lakes and wetlands in the state and are considered likely in 194 other water bodies connected to those lakes. Still, that’s only 408 out of 11,842 Minnesota lakes, or 3.5%.
Jensen says the fact that so few Minnesota lakes are infested 30 years after zebra mussels and Eurasian water milfoil came into the state is "remarkable," especially noting we have 866,000 registered boats (not including those from out of state) some 1.4 million anglers and more than 3,600 public boat landings that all serve as possible vectors to spread invasives. Throw in duck hunters, wakeboarders, scuba divers, dock installers and others who move between lakes and the potential of spread seems insurmountable.
But what Minnesotans have been doing, in most cases at a pretty good rate, is follow two decades of constant reminders to inspect, clean and drain their boats every time they take a boat out of a lake or river. We are reminded of the constant battle by messages on billboards, in the media and social media, on floating key chains, can-coolers, by state conservation officers and by AIS inspectors at boat landings.
Inspections show progress
In 2019, trained AIS boat inspectors for the DNR, counties, lake associations and other groups inspected more than 511,000 boats at landings across the state, by far the most ever. They found more than 96% of boaters were taking action to drain their boats to prevent moving AIS and 97% were removing weeds. That’s up from 71% compliance as recently as 2014. People are, for the most part, pulling weeds off their trailer, pulling their drain plugs out, emptying their livewells and disposing their leftover bait in the trash can at the landing when they leave.
Compliance was still decent, but fell off noticeably, at DNR random checkpoints set up without notice along highways popular for trailered boat traffic. At these roadside checkpoints compliance rates dropped to 81 percent on average in 2019 and were as low as 69% at one checkpoint along U.S. Highway 53 north of Duluth. Out of 84 trailered boats inspected that day, 11 owners were issued AIS citations (up to $250 each) and 15 were issued AIS warnings.
Still, the 81% compliance rate at roadside inspections is up from just 63% as recently as 2012, another sign that more boaters are getting the message and taking it more seriously.
“The trend is getting better. People are listening. People are taking action,’’ said Kelly Pennington, AIS prevention coordinator for the Minnesota DNR. “Most people are following AIS regulations, and that wasn’t always the case before.”
Not only does that prevent the spread of known invaders, Pennington noted, but every time someone removes a weed from their trailer or drains their livewell it means reduced risk of a new, as yet unknown invader being spread.
"People have bought us time. Most Minnesota lakes still are not'' infested with AIS, said Nick Phelps, director of the Minnesota Aquatic Invasive Species Research Center at the University of Minnesota. "The modeling shows us that it’s working. Far fewer lakes are impacted because people have taken action."
The effort hasn't been cheap. Last year the state spent $9.7 million on AIS education, control and enforcement efforts, not including university research. Much of that comes for the state’s general tax fund, with some from federal grants and the rest from the $10.60 AIS surcharge on all state boat licenses. The DNR spends some of that money. The rest is passed on to counties that dole out millions of dollars each year to lake associations and other groups for AIS projects across the state. (It's not yet clear how inspectors might be deployed this summer during COVID-19 restrictions.)
Jeff Forester, executive director of the Minnesota Lakes and Rivers Coalition, the statewide umbrella group advocating for lake associations across the state, said it’s great that more Minnesotans are taking AIS seriously. But he argues that too many holes still exist for AIS to slip through. It’s clear the battle is not over: Some 54 new water bodies were declared infested with zebra mussels in 2019 and 18 more reported Eurasian water milfoil invasions.
Forester advocates for mandatory inspections for all watercraft and water-related equipment entering the state, and he wants more and tougher penalties for people who violate AIS rules at boat landings or on the road. Minnesota’s future as the Land of 10,000 usable lakes, he said, is still at risk.
“If we have 31% violation rates on some roadside checks, we’re missing a big chunk of people with both the (education) message and the inspection. These (boats) are getting in and out of the lakes at marinas or lodges or other private landings where we don’t have inspectors,” Forester said.
Forester says some boaters still aren’t taking AIS seriously or don’t think it's worth the effort.
“We have 300,000 cabins and lake homes across the state but we have 6,000 members,’’ he said. “We need more people to develop a Minnesota lake ethic… to be as passionate about protecting the lakes as they are about using them.”
He also worries that, as more lakes become infested with a single invader, people will let their guard down, wrongly believing that there’s no point in protecting a lake that’s infested.
“What people need to know is that, while having one of these things is bad, having two or three of them can be exponentially worse. We don’t know which new (invader) is going to break it,’’ Forester said. “Look at Mille Lacs. Maybe it could make it with just spiny waterfleas or just zebra mussels. But combine the two and I don’t think we’ll ever see it come back the way it was for walleye fishing.”
Ask the experts what AIS they are most concerned about on the horizon and a few problems rise to the top. Snakehead fish, a nasty looking native of Asia and Africa with a voracious appetite, have been found in waters of California, Florida, Hawaii, Maine, Maryland, Massachusetts, Rhode Island, Virginia and Wisconsin.
Forester says he’s worried about a plant called water soldier, another Eurasian import already as close as southern Ontario, that forms in dense, impenetrable mats on the surface of lakes and can even change the chemistry of lake water.
Hydrilla, another native to Asia, is a fast, thick-growing plant that is choking out waters across the southern tier of states. It was first found in Florida in the 1950s, apparently released from aquariums, and is now growing as far north as Missouri.
Phelps says he’s most concerned with species that have recently arrived and have just taken hold, like Asian carp in the Mississippi River system and starry stonewort in lakes. “Those are the most likely to expand out of control very quickly. I worry that starry stonewort could go from 14 lakes today to 300 very quickly, like Eurasian water milfoil did.”
But Phelps also says he’s more optimistic than ever. Every day, he said, scientists get a little closer to developing tools to not just slow the spread but to fight back against invasives.
Later this summer officials will roll out a new tool, developed by researchers at the center, that can precisely predict what lakes are most at risk for new zebra mussel and starry stonewort invasions and which infested lakes are most likely to serve as the host for new invasions. Counties, lake associations and others will be able to check the data on a website showing the most likely pathways and station inspectors where they can do the most good.
“The boat inspectors are a great tool. We’ve seen the kind of compliance they get. But they can’t be everywhere,’’ Phelps said. “We now have the ability to strategically allocate resources to where they will do the most good.”
New treatment kills zebra mussels
While Phelps says education and prevention remain the best tools for now to slow invasives, he said the research center takes its mission seriously to develop tools to stop and even reverse invasions. He likened the AIS battle to the one against COVID-10: Determine the likely vectors, cut off the pathways with prevention and then work as fast as possible on a cure.
For AIS, that includes a four-year effort where scientists have been treating part of Lake Minnetonka near Minneapolis with a copper-based pesticide, or more precisely, a molluscicide. Slowly, at first in the lab and now in a real lake, they have been adjusting the amount of the material to kill as many zebra mussels as possible while not harming native species.
The most recent results from summer 2019, while still preliminary, were “amazing,’’ Phelps said. Across a 160-acre bay in the lake scientists were able to kill 100% of the tiny zebra mussel larvae, called veligers, and 95% of adult zebra mussels. The chemicals' impact on perch and other fish was minimal.
“We saw a little issue with some fathead minnows (succumbing to the treatment) but there was no impact on perch or other species. They will go back this year and see if they can dial in the right amount to eliminate any impact on non-targeted species,’’ Phelps said.
If successful on a broader scale the zebra mussel treatment could echo a similar effort, a chemical that’s been used to kill sea lamprey larvae in streams for the past 50 years. Annual use of that lampricide is considered the single largest factor in the rebound of Great Lakes fish populations.
The University’s AIS research center, created by the Minnesota Legislature in 2012, is now funding more than 60 researchers on 20 different projects, including scientists at the University of Minnesota Duluth and the Natural Resources Research Institute.
Next up, Phelps said, will be genetic modification of invasive species like carp and zebra mussels.
“The technology exists, in theory, to genetically modify them out of existence,’’ Phelps said. "I’m optimistic. Over the last 10 years or so the conversation about invasive species has changed. It’s not all about the end of times now. There’s some realistic hope out there.”
Minnesota AIS by the numbers: Some good news
8% of Minnesota lakes have verified invasive species.
3.5% of Minnesota lakes have verified zebra mussels.
97% of 511,000 boaters checked in 2019 at boat landings had removed weeds and vegetation from their trailer.
96% of 511,000 boaters checked in 2019 at boat landings had removed the drain plug and livewell water form their boat.
81% of trailered boats checked at DNR roadside checkpoints complied with state AIS laws.
95% of adult zebra mussels were killed by an experimental treatment in a 160-acre bay of Lake Minnetonka.
100% of zebra mussel larvae were killed in the same test project.
What’s so bad about:
Zebra and quagga mussels: Foreign invaders filter-feed microorganisms out of the water, removing key food for the native food chain. Remarkably clearer water looks good but can cause major disruptions in the ecosystem, sending some fish deeper and allowing more weeds to grow. They kill most all native clams and cover all smooth surfaces underwater, disrupting water supplies and forcing expensive cleaning efforts for underwater equipment.
Eurasian water milfoil: Chokes the shallow areas of lakes with dense growth, making boating, fishing and swimming difficult or impossible. Can be controlled with expensive, annual harvest and chemical treatment efforts. Easily spread from lake to lake by hitchhiking on boat trailers.
Starry stonewort: An algae new to Minnesota in the last decade that doesn’t need to be attached to lake bottom to thrive. Can grow in dense colonies in anywhere from 2 to 22 feet (which means all of some shallower lakes.) Nearly impossible to boat or fish in. Spreads easily and rapidly.
Spiny waterfleas: A tiny freshwater zooplankton that invade lakes, taking over the bottom of the food chain, disturbing the ecology of the lake. They can decimate populations of native zooplankton leaving less food for native fish and often causing an increase in algal blooms. Populations reproduce rapidly, up to 100 individuals per cubic meter, sometimes taking over the biomass of the lake. Many native predators won’t eat spiny waterflea because of their sharp, barbed spine.
Silver, bighead and grass carp: Can grow to 90 pounds and bigger, these so-called Asian carp species all filter-feed microorganisms out of the water thus disrupting the native food chain. Grass carp jump 10 feet in the air at the sound of a passing boat. They can overpopulate lakes and rivers and outcompete native fish for food. They have become the dominant species in parts of the Mississippi River in southern states. They have moved as far north as the Twin Cities in the Mississippi and into the Minnesota and St. Croix Rivers as well. They are at the cusp of entering the Great Lakes near Chicago.
Become an Aquatic Invasive Species Volunteer
Citizens who are interested in informing the public about aquatic invasive species and how to slow their spread can receive AIS volunteer training from Watercraft Inspection Program staff. Contact local DNR staff: Northeast Region: Keri Hull 218-203-4357 [email protected]; Northwest Region: Mike Bolinski 218-739-7576, ext. 259, [email protected]; Central and Southeast Region: Christine Hokkala-Huhns 651-259-5835 [email protected] ; Southwest Region: Travis Kinsell, 320-234-2550, ext. 247, [email protected].
See something unusual? Contact an expert
If you find something you suspect is an aquatic invasive species, plant or animal, note the exact location, take a photo or keep the specimen, and call a DNR AIS Specialist at 651-259-5100, or contact a local DNR office or University of Minnesota Sea Grant office. Go to mndnr.gov/ais for more information. Or try the University of Minnesota Sea Grant Program Aquatic Invasive Species Information Center 218-726-8712. For field guides, species profiles, articles, and AIS resources for teachers, visit seagrant.umn.edu.
You can also contact an expert in your region if you have questions on invasive species identification and management, purple loosestrife management and biocontrol, or prevention activities: Grand Rapids:,Richard Rezanka 218-328-8821; Brainerd, Tim Plude 218-203-4354; Park Rapids, Nicole Kovar 218-616-8102; Fergus Falls, Mark Ranweiler 218-739-7576, ext. 254; St. Cloud: Emelia Hauck Jacobs 320-223-7855.