Aquatic Invasive Species

Spiny water fleas appear as a gelatinous mass on a fishing line.
Spiny water fleas can be found in many Minnesota lakes including the 4 main lakes of Voyageurs National Park.

Voyageurs National Park aims to protect interior lakes from exotic species and fish disease

Exotic species such as the spiny water flea rusty crayfish, zebra mussel, and fish diseases are threats to the aquatic ecosystems of regional lakes including those in Voyageurs National Park. Spiny water fleas have recently invaded multiple lakes in the region, including the large lakes within Voyageurs National Park. Rusty crayfish have invaded at least one lake in Voyageurs National Park and many lakes in the region. Zebra Mussel were first detected in the fall of 2021 in Black Bay of Rainy Lake. Viral hemorrhagic septicemia (VHS), a fish disease, has not yet been introduced into any lakes in Minnesota, but has caused fish kills in most of the Great Lakes and in some inland lakes in Michigan and Wisconsin.

The Minnesota Department of Natural Resources (DNR) has designated the following water bodies as infested: Rainy Lake, Rainy River, Namakan Lake, Kabetogama Lake, Sand Point Lake, Crane Lake, and Little Vermilion Lake. The infested waters designation triggers specific Invasive Species Laws which can be found in the most current Minnesota DNR Fishing Regulations.

The National Park Service and DNR are working in concert to prevent the spread of the aquatic invasive species and fish diseases by:

· implementing Best Management Practices for visitors, partners, and staff

· conducting public education at boat launch areas about exotic species, invasive species laws, and Voyageurs National Park interim measures to prevent the spread of exotic species

· providing information about invasive species and fish diseases at park visitor centers, in park and DNR publications, and on the park website ( and the DNR website (

The National Park Service has adopted the following three interim measures to protect the interior lakes in Voyageurs National Park from exotic species and fish diseases:

· artificial bait only (on all interior lakes only)

· no privately-owned watercraft allowed in interior lakes (the park will continue to provide canoes and row boats for rent through the Boats on Interior Lakes program and Commercial Use Authorizations on Mukooda Lake)

· no float plane landings on interior lakes

If you plan to recreate on the interior lakes in Voyageurs National Park, please follow these best management practices:

· Bring a separate set of gear that is likely to contact lake water (including fishing gear) to use on the interior lakes, or before using any gear on an interior lake, make sure that all gear has been thoroughly dried for at least 5 days or washed with hot water (>140 degrees F) for at least one minute

· When leaving any lake, remove aquatic plants and animals, including gelatinous or cotton batting-like material from equipment, including fishing line

The park will conduct a program about exotic species and VHS for any interested party or organization.

To schedule a program call Tawnya Schoewe at 218-283-6670 or e-mail us.

With your help and careful actions, we can try to prevent the spread of zebra mussels, the spiny water flea, rusty crayfish, other invasive species, and fish diseases. Stop aquatic hitchhikers crossing from Rainy Lake to Namakan


Zebra Mussel

Zebra Mussel Fact Sheet

What’s Happening?
In late 2021, the Minnesota Department of Natural Resources identified zebra mussel veligers (larvae) in Black Bay of Rainy Lake and declared the lake to be infested. In response, Voyageurs’ staff is starting a zebra mussel containment and prevention program to protect other park lakes from invasion.

What Is Voyageurs’ Staff Doing?
Park staff are implementing several practices to keep zebra mussels out of Namakan basin lakes, these include:

  • Establishing a decontamination station at the Kettle Falls portage
  • Emphasizing the importance for visitors to follow Minnesota statutes implemented to minimize the risk of spreading invasive species
  • Allowing use of the Gold Portage for vessels traveling from Kabetogama to Black Bay of Rainy Lake only.
What Can Visitors Expect at Kettle Falls:
When crossing from Rainy Lake to Namakan Lake:
  • Boaters will be required to drain bait containers, live wells, ballast tanks, bilge areas, and any other water holds on vessels and equipment.
  • Be prepared to transport caught fish on ice from one lake to another.
  • Have a plan to maintain bait once bait containers are drained.
  • Trained staff will decontaminate all boats (including canoes and kayaks) with a washer using water heated to 140° F.
When crossing from Namakan Lake to Rainy Lake:
  • Boaters will be required to drain bait containers, live wells, ballast tanks, bilge areas, and any other water holds on vessels and equipment.
  • Be prepared to transport caught fish on ice from one lake to another.
  • Have a plan to maintain bait once bait containers are drained.
Why Does It Matter?
  • Ecosystem Harm: Zebra mussels can substantially harm aquatic ecosystems by reducing the health and populations of native fish and native mussels. For example, in Minnesota lakes infested by zebra mussels and spiny water fleas, the average size of first-year walleyes is 25% smaller than in uninfested lakes. This size decrease is concerning because there is evidence that smaller first-year walleyes have higher mortality rates than larger first-year walleyes.
  • Sport Fishing Implications: Voyageurs supports some of Minnesota’s most popular fisheries, accounting for more than 700,000 angler hours per year. The spread of zebra mussels throughout the park has potential to disrupt these fisheries. As spiny water fleas are already in the park’s large lakes, walleyes may be especially vulnerable.
  • Economic Loss: Zebra mussels can also cause significant economic loss resulting from clogged water intake systems, fouled boat motors, and reduced waterfront property values.
  • Expanding Invasion: From Rainy Lake in Voyageurs, it is possible to access Namakan Lake, and from Namakan Lake it is possible to reach other park lakes as well as lakes further east in the Boundary Waters Canoe Area Wilderness and Quetico Provincial Park. It is important to keep zebra mussels out of these pristine and protected areas.
Is it Worth the Effort?
Yes. The spread of zebra mussels is not inevitable; the Minnesota Department of Natural Resources estimates that less than 4% of lakes in the state are infested with zebra mussels.Preventing the spread of zebra mussels, and other invasive species maintains healthy habitats for native species. Healthy aquatic systems assure the health of native species, including popular sportfish.
Follow Established Procedures to Minimize Risk of Transport
Clean all visible aquatic plants, zebra mussels, and other prohibited invasive species from watercraft, trailers, and water-related equipment before leaving any water access or shoreland.
Drain water-related equipment (boat, ballast tanks, portable bait containers, motor) and drain bilge, livewell and baitwell by removing drain plugs before leaving a water access or shoreline property. Keep drain plugs out and water-draining devices open while transporting watercraft.
Dispose of unwanted bait, including minnows, leeches, and worms, in the trash. It is illegal to release bait into a waterbody or release aquatic animals from one waterbody to another. If you want to keep your bait, you must refill the bait container with bottled or tap water.
Spray, rinse, dry — Some invasive species are small and difficult to see at the access. To remove or kill them, take one or more of the following precautions before moving to another waterbody, especially after leaving zebra mussel and spiny waterflea infested waters:
  • Spray with high-pressure water
  • Rinse with very hot water*
  • Dry for at least 5 days

* These water temperatures will kill zebra mussels and some other AIS: 120°F for at least 2 minutes; or 140°F for at least 10 seconds.

For more information, see the Superintendents Compendium II. 36 CFR 1.5 (a)(1). Superintendent's Compendium - Voyageurs National Park (U.S. National Park Service) (


Spiny Water Flea

Spiny water fleas can be found in many Minnesota lakes including the 4 main lakes of Voyageurs Naitonal Park.  They are tiny (1/4-5/8") crustacean zooplankton native to Eurasia and were introduced into the Great Lakes from the ballast water of ships. They threaten the park's aquatic ecosystems and fishing by competing with native fish for food and fouling fishing gear. Research has shown that the spiny water flea can cause the following impacts:

· change the community composition of zooplankton

· compete directly with juvenile yellow perch and other small fish and minnows for food which could lead to a decrease in the abundance of these fish

These impacts could alter the food web; for instance, yellow perch are an important part of the diet of walleye, so a decrease in yellow perch abundance could hurt walleye growth.

Spiny water fleas are spread when either live adult water fleas or viable resting eggs are transferred to a new body of water. Spiny water fleas and viruses that cause fish diseases can be transported on bait buckets, anchor ropes, fishing line, boats, waders, and nets. Any gear that enters infested water and is transferred to another lake or river without being thoroughly dried (for at least 5 days) or washed with hot water (>140° F for at least one minute) could transfer exotic species and fish diseases.


Rusty Crayfish

Rusty crayfish are native to the Ohio River drainage but have invaded lakes in Wisconsin and Minnesota in recent years. They were found in Sand Point Lake in 2006. Rusty crayfish are more aggressive than native crayfish and can eliminate native crayfish and aquatic plants, causing great change to the aquatic ecosystem of invaded lakes. Please do not move live crayfish from one lake to another, and remember that it is illegal to use live crayfish for bait in any lake in Voyageurs National Park.

Viral Hemorrhagic Septicemia

Viral hemorrhagic septicemia (VHS) is a viral fish disease that has been found in all of the Great Lakes except Lake Superior. It can kill many species of game fish including walleye and muskellunge. It could easily be spread to Minnesota lakes since many people travel between areas with infected lakes and Minnesota, and the virus that causes the disease can be spread by moving infected bait or water to uninfected lakes. Although VHS causes mortality in fish, it is not a threat to human health.

Last updated: April 15, 2022

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