Department of Natural Resources (DNR) biologists fear they might be seeing a disturbing trend of zebra mussels hitchhiking on boat lifts that are moved from infested waters to uninfested lakes. The second such case was discovered this week on the northeast corner of Lake Irene in Douglas County, where a localized population of zebra mussels was discovered on a lift last weekend.
A similar case was discovered at Rose Lake in Otter Tail County Sept. 28.
DNR staff members were called to property on Lake Irene Oct. 8 to investigate the presence of zebra mussels on a boat lift that had recently been removed from the water. They suspect the zebra mussels were transported to the lake this summer when the boat lift was moved in from an infested lake.
"Moving docks and boat lifts from zebra mussel infested lakes to other lakes is a serious issue," said Nathan Olson, DNR invasive species specialist in Fergus Falls. "We can't stress enough that everyone needs to take extra precautions to avoid transporting these pests to other state waters."
An inspection revealed clusters of mussels on the feet and inside the tubing of the boat lift. No additional zebra mussels were found after inspections of 74 additional Lake Irene boat lifts and docks near the infected boat lift.
The next day a diver searched the bottom of the lake where the boat lift was located and found zebra mussels attached to rocks. The mussels were found only in the immediate area where the boat lift was located.
The DNR plans to treat the small area with copper sulfate, a common chemical used to treat snails that cause swimmers itch. The treatment could be conducted by a licensed aquatic pesticide contractor early next week.
"As with Rose Lake in Otter Tail County, we are hoping that early detection and rapid response to the zebra mussel discovery might prevent an infestation," said Olson. "We won't know for sure if treatment is successful until next summer."
The DNR will designate Lake Irene as an infested water body. This designation adds additional restrictions for the transport of water from the lake and prohibits bait harvest on the lake. It also means there will be increased enforcement and watercraft inspections efforts in this area.
This will be the seventh lake the DNR has designated as infested with zebra mussels in 2011.
The introduction of the zebra mussels into Lake Irene and Rose Lake is being investigated by area DNR conservation officers. It is illegal to possess, import, purchase, sell, propagate, transport or introduce invasive species into Minnesota waters. Violators can receive civil and criminal penalties.
Boat lifts and docks are of particular concern because they sit in the water for extended periods, giving adult zebra mussels a greater opportunity to attach themselves.
"We strongly recommend that all water-related equipment be cleaned thoroughly by pressure washing with hot water and dried for a minimum of two weeks before putting the equipment into a body of water," Olson said. "It's imperative that people act responsibly to slow the spread of aquatic invasive species."