DNR wins a round in battle against zebra mussels

Divers found no evidence of zebra mussels.
A survey by divers of Christmas Lake in Hennepin County found no evidence of zebra mussels on April 13, 2015.
Courtesy Minnehaha Creek Watershed District

Minnesota natural resources officials appear to have won a skirmish in their long, ongoing battle against invasive zebra mussels.

A three-step treatment to kill a pocket of mussels in Hennepin County's Christmas Lake has been effective on a "small, isolated infestation" that was detected early," the state Department of Natural Resources said Monday.

An April 13 survey by divers found no evidence of zebra mussels.

"We are encouraged by these early results," Keegan Lund, DNR aquatic invasive species specialist, said in a statement. "We used every available tool to respond to this isolated zebra mussel infestation and learned valuable information in terms of responding to new infestations."

Cluster of mussels
A cluster of zebra mussels rested on a piece of driftwood.
Ann Arbor Miller | For MPR 2012

The DNR began its treatment of Christmas Lake in September. It took a new approach, using a product called Zequanox, which is made from the dead cells of a naturally occurring microbe.

The company that makes the product says that once ingested, it deteriorates a mussel's digestive lining, causing death without harming the rest of the ecosystem.

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Besides Zequanox, the DNR used a copper treatment of EarthTec QZ in both October and November. A month later, a contractor working with the DNR injected 1,000 pounds of potash under the ice near the public boat access.

The copper and potash applications were "experimental off-label uses," the DNR said.

"Extensive in-lake monitoring will be required over a period of years to determine whether zebra mussels have been eliminated from the lake," the department added.

More than 175 Minnesota lakes and rivers are infested with zebra mussels, an invasive species that can push out native mussels. They can also cause more algae and weed growth — they filter the lake water, allowing sunlight to penetrate more deeply. They attach to boats, making it easy for them to travel and contaminate other waters.

In 2012, the DNR tried a copper sulfate treatment in lakes in Otter Tail and Douglas counties but the experiment failed.