ST. PAUL - Zebra mussels have been confirmed in Union Lake near Erskine, Minnesota, in Polk County, the Department of Natural Resources said Monday, July 15.
The invasive mussels also were confirmed in First Silver Lake near Battle Lake in Otter Tail County and Heilberger Lake near Erhard, also in Otter Tail County, the DNR said.
In a news release, the DNR said a property owner contacted the DNR after finding a zebra mussel attached to a native mussel in Union Lake. DNR staff found more than 15 zebra mussels near the public water access, which is more than a mile from the location of the initial discovery, the DNR said.
Union Lake has a pump that is used in certain high-water conditions. This pump already has a filter to prevent the dispersal of Eurasian watermilfoil - also an invasive species - the DNR said, and is not currently operating. The DNR said it will provide direction to the Sand Hill River Watershed District, which operates the pump, to ensure that any future pumping operations are modified to also meet filtration requirements to prevent the spread of zebra mussels downstream.
Covering 887 acres, Union Lake is a popular destination for residents of Grand Forks, East Grand Forks and the surrounding area. The lake is best known for its walleye, bass and panfish opportunities. Based on results from the DNR's most recent fisheries assessment in August 2022, walleye abundance has declined from record highs in 2012, but catch gill net catch rates, at 6.3, were only slightly below the historical average of 6.8 per net. Walleyes ranged from 7.7 inches to 30.1 inches with an average size of 19 inches.
Pike catches set a record in 2022, the DNR said, at 11.9 fish per net, nearly double the historical average of 6.1. Pike averaged 15.1 to 32 inches in length with an average size of 21.9 inches.
Bluegill catches in 2022 declined, the DNR said, with an average catch rate of 8.3 per net compared with the historical average of 36.6. Crappie abundance was up slightly, at 3.6 per net, with an average size of 8.7 inches and fish up to 12.1 inches sampled.
Largemouth bass, at 1.8 per net, averaged 11.5 inches long with bass up to 18.1 inches long sampled. Perch abundance was low, with an average length of 6.3 inches, the DNR said.
In its news release, the DNR said the infestation on First Silver Lake in Otter Tail County was confirmed after a lake user brought two zebra mussels to a DNR office and provided details on where they were found. A DNR invasive species specialist then found two zebra mussels on the public water access boat ramp, about three-quarters of a mile from the location of the initial report.
On Heilberger Lake, a lake property owner contacted the DNR after finding three zebra mussels attached to a native mussel. A subsequent search by a DNR invasive species specialist found five zebra mussels on the public water access boat ramp, about a quarter-mile from the location of the initial report.
While zebra mussels and other invasive species can be introduced to a lake via private docks and accesses, public accesses are typically the first to be surveyed for invasive species.
Whether or not a lake has any invasive species, Minnesota law requires people to:
These additional steps reduce the risk of spreading aquatic invasive species:
People should contact a Minnesota DNR aquatic invasive species specialist - mndnr.gov/invasives/ais/contacts.html - if they think they have found zebra mussels or any other invasive species that was not already known to be in the water body.