Photo: Dave Britton, USFWS

From the Minnesota Department of Natural Resources - November 12, 2019

The Minnesota Department of Natural Resources has confirmed zebra mussel larvae in water samples taken from one of three sites in Lake of the Woods on the northern Minnesota border. While no adult or juvenile zebra mussels have been reported, the number of larvae is substantial.

The Minnesota portion of Lake of the Woods will be added to the infested waters list for zebra mussels, so that people who harvest bait, fish commercially or use water from the lake take necessary precautions. Other lake users should follow the same “Clean, Drain, Dispose” steps that are always legally required on all Minnesota water bodies, regardless of whether they are on the infested waters list.

Recent DNR analysis of large lake zooplankton monitoring samples showed from four to 186 zebra mussel larvae, called veligers (VEL-uh-jers). “We don’t know if the lake’s water chemistry is conducive to zebra mussel survival,” said DNR research scientist Gary Montz. "It is possible that calcium levels or other factors might prevent propagation.”

The DNR and other agencies will continue to monitor the lake, in part to learn more about how the lake’s water chemistry affects zebra mussels. The invasive species spiny water flea was confirmed in Lake of the Woods and connected waters in 2007. Invasive species are sometimes introduced in a lake from connected waters or tributaries rather than human transport directly into the lake.

The 70-mile long and wide Lake of the Woods is the sixth largest freshwater lake located in or partially in the United States, after the five Great Lakes. Most of Lake of the Woods is in the Canadian Province of Ontario, and a portion extends into the Province of Manitoba.

Lake property owners should carefully check boats and trailers, docks and lifts, and all other water-related equipment for invasive species when removing equipment for seasonal storage.

It is especially important to follow Minnesota’s law and keep docks and boat lifts out of the water for at least 21 days before putting them into another body of water.

Anyone transporting a dock or lift from a shoreline property to another location for storage or repair may need a permit  to help prevent the spread of aquatic invasive species.

The DNR recommends these steps for lake property owners:

• Look on the posts, wheels and underwater support bars of docks and lifts, as well as any parts of boats, pontoons and rafts that may have been submerged in water for an extended period.
• Hire DNR-permitted lake service provider businesses  to install or remove boats, docks, lifts and other water-related equipment. These businesses have attended training on Minnesota’s aquatic invasive species laws and many have experience identifying and removing invasive species.

People should contact an area DNR aquatic invasive species specialist  if they think they have found zebra mussels or any other invasive species.

Whether or not a lake is listed as infested, Minnesota law requires boaters and anglers to:

• Clean watercraft and trailers of aquatic plants and prohibited invasive species,
• Drain all water by removing drain plugs and keeping them out during transport, and
• Dispose of unwanted bait in the trash.

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:     

• Spray with high-pressure water.
• Rinse with very hot water (120 degrees for at least two minutes or 140 degrees for at least 10 seconds).
• Dry for at least five days.

Zebra mussels can compete with native species for food and habitat, cut the feet of swimmers, reduce the performance of boat motors and cause expensive damage to water intake pipes.

More information is available at mndnr.gov/ais .