Zebra mussels have invaded Gull Lake, one of the Brainerd area's more popular lakes.

"It's really unfortunate,'' said Dan Swanson, Department of Natural Resources invasive species specialist. "It's a premier lake, used by a lot of people for fishing, boating, swimming and other recreation.''

The infestation is a blow to the Brainerd Lakes area and Gull Lake residents, who have tried to prevent the spread of zebra mussels. The impact to infested lakes varies, but the mussels filter vast amounts of water, which can affect water clarity, vegetation growth and thus possibly fisheries.

"What will happen is unpredictable,'' Swanson said.

The discovery underscores the likelihood that zebra mussels will continue to spread throughout Minnesota's lakes and rivers, despite efforts to educate boaters to drain their bilges and livewells when leaving lakes. In the past two years, the tiny mussels have been found in some of the state's bigger and more heavily used lakes, including Mille Lacs, Minnetonka, Prior and Le Homme Dieu, and in parts of the Mississippi, St. Croix and Zumbro rivers.

"There's definitely been a major expansion of zebra mussels in the last two years, there's no denying that,'' Swanson said.

Swanson said he got a call Monday from a company that found zebra mussels on docks and boat lifts it was removing from the west side of Gull Lake. Swanson also found mussels on vegetation there. On Tuesday, more mussels were found on the east side, meaning they probably have spread throughout the lake.

The DNR now will designate Gull as infested waters, which prohibits the transport of water and requires draining of all water, including bait containers, and also prohibits harvest of bait. Signs also will be placed at water accesses, and there will be heightened enforcement and watercraft inspections.

But those efforts have been made elsewhere, and the mussels continue to spread.

Native to Eastern Europe and Western Russia, zebra mussels were first discovered in Minnesota in 1989 in the Duluth harbor.

Doug Smith • 612-673-7667