Thirty-five years ago, in 1989, the first zebra mussels arrived in Minnesota in Lake Superior’s Duluth Harbor. The mussels are native to Eastern Europe and Western Russia but were unintentionally introduced into the Great Lakes via contaminated ballast water in a cargo ship. Five years later, zebra mussels were found in Minnesota again, this time in the Mississippi River. Since then, zebra mussels have spread to 359 inland lakes, with an additional 270 connected water bodies also considered infested. Fourteen new zebra mussel infestations were discovered in Minnesota in 2024, including Big Carnelian Lake in northern Washington County.
Zebra mussels pose a huge economic, environmental, and recreational threat because of their ability to spread rapidly and adhere to underwater surfaces, including boats, docks, water-intake pipes, and even native freshwater mussels. A female can produce 100,000 to 500,000 eggs per year, and these eggs hatch into microscopic larva, known as veligers, which float through the water and are impossible to see. Unfortunately, it is virtually impossible to eradicate zebra mussels once they are present in a lake or river.
The zebra mussels in Big Carnelian were first reported by a concerned resident, who found a mussel off the shore of their family’s property in early August. The following day, staff from the Minnesota DNR, Washington Conservation District, and Carnelian-Marine St. Croix Watershed District organized a rapid response effort, which included searching multiple locations in the lake with scuba diving, snorkeling, and wading equipment. In addition to finding dozens of adult zebra mussels, staff also found microscopic veligers in lake water samples. Given the number and widespread occurrence of adult and larval mussels found in Big Carnelian, the DNR concluded that the zebra mussel population has been present for at least three years and that there are no effective treatment solutions available.
While news of a new zebra mussel infestation is discouraging, it is important to remember that 96% of lakes in Minnesota do NOT have zebra mussels and can still be protected from future infestations if lakeshore landowners, contractors, boaters, and anglers commit to taking action.
One of the key strategies local communities use to prevent invasive species from spreading to new lakes and rivers is to conduct watercraft inspections at boat launches and water access points. Watercraft inspectors are specially trained to identify invasive plants and animals such as curlyleaf pondweed, Eurasian watermilfoil, zebra mussels, and spiny waterfleas and are able to teach boaters how to properly clean and drain trailers, boats and personal watercraft. (Minnesota law requires people to clean all visible plants, mud, and mussels from their watercraft and drain ballast tanks, portable bait containers, drain bilge, livewells and other compartments before they leave a water access.)
When the Washington Conservation District (WCD) first began conducting watercraft inspections in 2015, they noted that most people were doing a good job of cleaning their boats but 7% were failing to drain their boats and equipment – a major concern for invasive species like zebra mussel veligers and spiny waterflea, which can be transported in water. Thanks to a robust watercraft inspections and education program, this statistic has improved tremendously during the past decade. Last year, less than 1% of incoming boats at Washington County launches had plants or mud attached, and WCD watercraft inspectors only found one boat with a zebra mussel attached.
Unfortunately, public boat launches are not the only transmission pathway for zebra mussels to spread. Many boaters launch from private residences or privately owned marinas. Zebra mussels can also be spread by water service providers installing or removing boats, docks, and lifts, as well as by contractors installing rock rip rap and retailing walls.
If you own lake or riverfront property, be careful to only hire contractors that are on the Minnesota DNR’s list of permitted service providers (bit.ly/MNDNR_LSP) and consider pooling funds with neighbors to hire a single service provider to reduce the number of visits from contractors this fall. Lake service providers should have a protocol in place to clean, inspect, and decontaminate their equipment after leaving a lake or river and should be extra cautious when working on water bodies with known infestations.
East metro area lakes with zebra mussel infestations include:
- Washington County: Big Carnelian, Bone, Forest, and White Bear Lakes, and the St. Croix River downstream of the Boom Site (River Mile 25.4)
- Chisago County: Comfort and Little Comfort Lakes
- Ramsey County: Bald Eagle, Charley, Johanna, Long, McCarron, Owasso, Pleasant, Sucker, and Vadnais Lakes
- Isanti County: Spectacle Lake.
Learn more about aquatic invasive species in Minnesota at www.dnr.state.mn.us/invasives/ais.
East Metro Water 