FOREST LAKE, Minn. - Zebra mussels have moved into Forest Lake.

The Minnesota Department of Natural Resources reported Friday that the invasive species has been found in several parts of the popular northern Washington County lake.

The lake will be designated as infested, which will bring new enforcement efforts designed to limit the spread of the zebra mussels.

DNR biologists inspected the lake after a visitor found a zebra mussel on a rock last week. They found additional mussels and said the population probably is well established and reproducing. For that reason, the DNR said it doesn’t plan to treat the lake.

Heidi Wolf, the DNR’s invasive species unit supervisor, said that “under 200” Minnesota lakes and rivers are known to be infested by the zebra mussel or linked to infested waterways.

Many of the state’s major bodies of water already are home to zebra mussels, including the Mississippi and St. Croix rivers, and Minnetonka and Mille Lacs lakes. The Forest Lake infestation is the fourth to be confirmed this year.

Zebra mussels are one-quarter inch to 1½ inches long. A single female can produce up to 500,000 eggs annually, according to the DNR. The eggs develop into tiny larvae that attach to solid objects, including boats.

The small mussels reproduce rapidly, coating the bottoms of lakes and rivers with sharp shells than can cut swimmers’ feet. They can choke water intake pipes for power plants or water utilities. They eat plankton, denying food for other species.

The “infested” designation will mean changes for Forest Lake.

Wolf said warning signs have been put up at access points, and more inspectors will be assigned to monitor boat traffic between lakes and to inform boaters about the potential harm of the mussels.

Wolf said the spread of zebra mussels is preventable. Fewer than 5 percent of Minnesota’s rivers and lakes are infested - an indication that most boaters are taking proper precautions, she said.

To prevent the spread of zebra mussels, boaters should not move infested water in any form. That means removing the drain plugs from boats and keeping them out while traveling. In addition, unused bait should be disposed of in the trash.

The DNR also recommends boaters clean aquatic plants and debris from the hulls of boats. Before putting a boat into another lake, the DNR suggests that a boater wash it with high-pressure washers or hot water.

An alternative is to let boats and equipment dry for at least five days before launching them into another river or lake.

Earlier this week, North Dakota’s Game and Fish Department reported that young zebra mussels had been found for the first time in the Red River north of Wahpeton, N.D.

A survey conducted by the department in June found a “significant” number of zebra mussel larvae at Wahpeton, Abercrombie, Fargo, Grand Forks, Drayton and Pembina.

Zebra mussel larvae were found in the Wahpeton area in 2010, 2011 and 2014, but not north of the city. The Red River flows north.

The only known population of zebra mussels within the Red River basin is an established population of adults in the Otter Tail River watershed in Minnesota, upstream from where the Otter Tail and Bois de Sioux rivers join to form the Red at Wahpeton-Breckenridge.

Biologists now wonder if there are undiscovered colonies of adult zebra mussels elsewhere within the Red River watershed.

The Pioneer Press is a media partner with Forum News Service.

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