Zebra mussels found in Crooked Lake, 10 miles south of BWCA

Zebra mussels have been found clustered on an aluminum can in an isolated lake in northeastern Minnesota, a leap of possibly 70 miles for the invasive species to within shouting distance of the Boundary Waters Canoe Area Wilderness.

Biologists from the Fond du Lac Band of Chippewa, who were examining fish in Crooked Lake, about 12 miles northeast of Finland, near the border between Lake and Cook Counties, found the can in recent days.

Workers from the Minnesota DNR and the U.S. Forest Service have not found other mussels since then, despite using underwater cameras, sediment samples, rakes, sonar and plain old walking searches. But the lake will be managed as infested, and crews will continue to search connected waters.

"Nothing anymore is a surprise, but it is a disappointment," said Rich Rezanka, aquatic invasive species specialist for the DNR. "We've tried hard with prevention methods. Someone wasn't paying attention.

"[The zebra mussels] didn't drive up there or hitchhike up there. They got moved up there."

Crooked Lake is about 10 miles north of Lake Superior, which because of a low nutrient content has few zebra mussels, and the same distance south of the BWCA, a million-acre roadless area where none has been found. The nearest infestation of an inland body of water is in a reclaimed ore pit near Gilbert, about 70 miles west of Crooked Lake, which is accessible from a single boat landing on a forest road.

Zebra mussels filter nutrients from lake water, leaving it clearer but with less food for fish and other native aquatic species. Boundary Waters lakes are popular for fishing but are low in nutrients to begin with, so a zebra mussel infestation there would likely damage fish populations, Rezanka said.

Landings at busy lakes are often staffed by DNR inspectors who look for boats that might be carrying zebra mussels or their microscopic larvae from infested lakes. The Crooked Lake landing had no inspector, Rezanka noted. Boaters are frequently urged to clean boat hulls and pull drain plugs when moving boats from lake to lake, and to put bait from one lake into water from another source, such as a well, before using it on another lake.

The Crooked Lake discovery comes 25 years after zebra mussels were first found in Minnesota, in Duluth-Superior Harbor, in 1989. Natives of Eastern Europe and western Russia, they were likely transported to central North America in the ballast water of oceangoing freighters.

Since 1989, they have spread throughout the Great Lakes and Mississippi River watershed, as well as to numerous inland lakes and streams in nearly two dozen Minnesota counties. Infested waters include popular lakes in the Brainerd area, Lake Mille Lacs, Lake Minnetonka and Minnehaha Creek.

The fingernail-sized zebra mussels are the only freshwater mussel that can attach to objects. Female zebra mussels can produce up to half a million eggs per year. As a result, they have been known to clog water intakes and form masses on boats, nets, docks, swim platforms and boat lifts. They also can attach to aquatic plants, and their sharp shells have been known to cut people's bare feet.

Zebra mussels begin to spawn in water that's in the middle 50-degree range, with activity reaching a peak in late June and early July, which brings the greatest chance of the mussels being moved from lake to lake, Rezanka said.

Bill McAuliffe • 612-673-7646