DNR: New treatment aims to eradicate Christmas Lake zebra mussels

In an effort to eliminate any remaining zebra mussels from Christmas Lake in Shorewood, the Minnesota Department of Natural Resources has undertaken an experimental treatment that has been used only twice before in the U.S.

On Friday, Dec. 19, a contractor working with the DNR injected 1,000 pounds of potassium chloride under the ice near the public boat access on the northwest corner of Christmas Lake. The chemical – also referred to as potash – kills zebra mussels by interfering with their ability to breathe, but it does not affect fish.

The potash application is the third treatment at the lake, where a small number of zebra mussels were found in August as part of the Minnehaha Creek Watershed District’s early detection monitoring program. Because the mussels were found early and were confined to a small area, DNR staff thought it feasible that treatment might eliminate them. The DNR and the district have subsequently treated the affected portion of the lake with Zequanox, a substance made up of dead bacteria, and later with a copper-based chemical.

“We’re trying all available options at Christmas Lake as the zebra mussel infestation was isolated to a small area of the lake,” said Keegan Lund, an invasive species specialist for the DNR. “Most importantly, we’re learning a lot about new treatment methods for zebra mussels that have not been used before in lakes.”

This treatment is only the third time that potash has been used for zebra mussel control in the United States. Because the chemical is not a federally registered pesticide, the DNR first needed to obtain authorization from the U.S. Environmental Protection Agency under an emergency exemption. Potash then needed to be registered as a pesticide with the Minnesota Department of Agriculture. The Minnesota Pollution Control Agency also reviewed the potash treatment plan and did not find immediate water quality concerns with the proposal.

If successful, the efforts at Christmas Lake could become the first time zebra mussels have been eradicated from a Minnesota water body, providing valuable information on treatment options when the invasive pests are discovered early.

A potash treatment may also be tried next spring on Lake Independence, where zebra mussels were found in October at the Baker Park Reserve boat launch. Both lakes will continue to be monitored to determine if the treatment s were successful.

Zebra mussels are an invasive species that can crowd out native mussels and compete for food sources with other aquatic animals such as larval fish. They attach to boat hulls and other water-related equipment and can create a hazard for swimmers due to their sharp shells.

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