Pesticide treatment on zebra mussels may work in one northern lake

Jodie Hirsch
Diver Jodie Hirsch, an invertebrate biologist with the Minnesota Department of Natural Resources, checks a boat dock for zebra mussels in Rose Lake on Wednesday, Sept. 5, 2012. Rose Lake is located about 10 miles east of Detroit Lake in northern Minnesota and was treated with the pesticide copper sulfate last fall. The DNR is currently monitoring Rose Lake, but so far it appears efforts the pesticide is working to halt a zebra mussel infestation.
MPR Photo/Ann Arbor Miller

An experimental effort to stop the spread of zebra mussels in a northern Minnesota lake might be working, according to the state Department of Natural Resources.

This week, divers searched for zebra mussels in a small lake in Otter Tail County. Last fall, a small area of the lake was treated with chemicals to kill the invasive aquatic species.

DNR Research Scientist Gary Montz is one of two divers searching a small area at a resort on Rose Lake. Clad in scuba gear, he scans the underside of a dock looking for zebra mussels.

Zebra mussels likely arrived at Rose Lake last summer on a boat lift that came from a nearby lake that was already infested. A few weeks later, a local resident noticed the invasive species and contacted the DNR.

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Because the infestation was new and appeared to be confined to a small area, the DNR decided to treat the area with a pesticide last fall.

This case is a unique situation where the zebra mussels were found quickly, and hopefully before they spread, said DNR Invasive Species Specialist Nathan Olson.

"We're hoping we don't see any zebra mussels, is what we're hoping today. That's just going to be another step in the right direction for us," Olson said. "We haven't seen any baby zebra mussels in any of our water samples yet this summer."

"It's a positive sign but we still need to monitor the lake down the line."

A Fargo man was charged with transferring the zebra mussels to Rose Lake. Earlier this year he paid $1,000 in fines and restitution.

The DNR also used pesticide on a lake in Douglas County where zebra mussels were brought in on a piece of equipment. A man charged in that case is set to go to trial next week.

A new law requires any equipment taken from a lake to dry for 21 days before it can be moved to another lake.

The DNR divers emerge from the lake after a couple of hours. They found no zebra mussels. But that doesn't mean they aren't out there, Montz said.

"It's really difficult because you're looking for something that may only be a half-inch long. We didn't find any," Montz said. "It's a positive sign but we still need to monitor the lake down the line."

Montz says even if the pesticide treatment successfully stops the zebra mussel infestation at Rose Lake, that doesn't mean the treatment would work on other lakes. Rose Lake is unique because the zebra mussels were discovered soon after they were introduced to the lake.

Olson is pleased the divers found no zebra mussels, but he's not ready to call this experiment a success.

"From my experience with zebra mussels, they seem to have a really big increase in about two years,once they're found in a lake," Olson said. "If I don't see any zebra mussels for about two years, then I'm going to be more excited about our success rate."

Olson said he will return this fall to check for zebra mussels on docks and boat lifts, after residents pull the equipment out of the lake for the winter.

That's something he said all Minnesota lake residents should make part of their fall routine as they close up their cabins.