New Study: Zebra Mussels Widespread in Lake Minnetonka

A new survey shows a widespread zebra mussel presence in Lake Minnetonka.

In just the first month of surveying, the Minnehaha Creek Watershed District found the invasive species at 24 of 32 monitoring sites. Making matters worse, the shutdown of state government has temporarily halted all invasive species inspections at Lake Minnetonka’s boat accesses.

That worries Kelly Dooley, a district water quality technician, who said Wednesday morning that critical education and data collection opportunities are missed each day the Department of Natural Resources isn’t in the field. Boaters on the lake now have to handle inspections themselves, Dooley said.

"I think everyone, not just the Minnehaha Creek Watershed District, wants to see the DNR back,” she said.

A dense population of zebra mussels filters out plankton in the water column that fish and other native species feed on, altering the lake's food chain. As zebra mussels age and die, their razor-sharp shells wash ashore and coat previously sandy beaches. Dense clusters can also weigh down docks and piers, creating safety and architectural problems.

Zebra mussels, native to the Soviet Union, migrated to Minnesota through the ballast water of transoceanic boats entering the Great Lakes. Infestations have been confirmed in about two dozen Minnesota lakes. 

Zebra mussels were likely present for at least a year prior to their discovery on Lake Minnetonka last summer, Dooley said. With no natural predators or practical pesticides, conservation officials can only hope to contain the infestation and educate boaters.

“Our main concern is zebra mussels leaving Lake Minnetonka and going to another lake that is just as vital as Lake Minnetonka in our watershed district,” Dooley said.

Wayzata resident and frequent Lake Minnetonka boater David Gondeck-Becker has seen firsthand how fast zebra mussels have spread in his home lake. Yesterday he found three on milfoil picked up by his boat. While frustrated that the state shutdown halted inspections for invasive species, Gondeck-Becker conceded that at this point they would have little impact on the zebra mussel population in Lake Minnetonka.

“To be realistic, I think it’s going to be almost impossible to keep (them contained) unless you just basically keep other boats from going onto other lakes, which I know is some talk out there,” he said. “It’s tough. I don’t know how you avoid it. All it takes is one boat.”

Bill Ashenbach of Minnetonka was launching his boat into Lake Minnetonka Wednesday morning. Doing his part to quell the spread of zebra mussels has become part of his boating routine.

“I know we’ve got to watch our boats and our weeds,” he said. “We use the lake all the time and wash everything down when we’re done.”

The Minnehaha Creek Watershed District has launched a three-year study to monitor the spread of zebra mussels in Lake Minnetonka and gauge the density of their population. Monitoring devices have been installed at 32 sites around the lake. So far, Halsted Bay, Harrisons Bay, Coffee Cove, Wayzata Public Dock and Casco Point are the only stations where the mussels haven't been found. Monitoring devices at three other locations were lost and have been replaced.

Officials expect the study to provide additional data, including insight into the density of the lake's mussel population, by summer's end.