Zebra mussels found in metro lake

Zebra mussels have found their way into a large east metro lake, joining dozens of other Minnesota lakes infested with the aquatic invasive species.

A lake user found a quarter inch-long zebra mussel in Washington County's Forest Lake, the Minnesota Department of Natural Resources said Friday.

All told, the DNR located at least 11 adult zebra mussels on the eastern and southern shores.

"Finding them on two different shores showed us that they were widespread," DNR invasive species unit supervisor Heidi Wolf said. "It's definitely an established population within the waterbody."

Forest Lake is the fourth Minnesota Lake with newly discovered zebra mussels in 2015. This summer, the DNR found them in Fishtrap Lake in Morrison County, Lake Eunice in Becker County and in late spring in Hennepin County's Christmas Lake.

Christmas Lake had been treated and declared free of zebra mussels. In May, the DNR said it found a new population outside the treatment area.

Steve Schmaltz, board manager of the Comfort Lake-Forest Lake Watershed District, said an enforcement program has kept the invasive species out of Forest Lake for the past seven years.

The watershed district, along with the city of Forest Lake and the Forest Lake Association, has funded 500 to 1,500 annual boat inspection hours. This year they've more than doubled scheduled hours to 3,100 hours.

"It's kind of ironic that this year when we ramped up the coverage it actually enters the lake," Schmaltz said. "It points out the fact that even though you do a lot of protection people really transport the invasive species into the lakes."

More than 200 Minnesota bodies of water are infested with zebra mussels, according to the DNR.

The aquatic invasive species is easily transported on boats and other watercraft if they're not cleaned properly.

"It only takes one boat to have a zebra mussel in it to cause a problem," Schmaltz said. "It's pretty difficult to keep them out."

The DNR has trained a total of 652 boat inspectors this year, the highest number ever, according to Wolf.

Inspectors are often at the lakes during summer weekends to talk to boaters about aquatic invasive species and stop some from launching with zebra mussels attached.

Zebra mussels interrupt the food chain and eat food that larval fish might eat. They hang on to hard surfaces including vegetation and stick to boat parts and engines.

The best way to avoid transferring them is to let boats dry for at least five days to kill zebra mussels before entering another lake.

By state law, boaters must clean boats thoroughly, drain all lake water out and dispose of any unwanted bait instead of releasing it back into the water.

The Comfort Lake-Forest Lake Watershed District has been monitoring Forest Lake for zebra mussels for a few years. A consultant told the board an invasive mussel population would grow relatively slowly given the natural design of the lake.

"It all depends on the chemistry of the water and the amount of food available," Schmaltz said. "When you look at all those factors, they assume that it's going to be moderate growth in Forest Lake."

The DNR is not planning treatment for Forest Lake or any other infested lake that's larger than 11 acres.

Forest Lake is more than 2,000 acres. No research has provided effective treatment for large bodies of water with zebra mussels spread throughout, Wolf said.

"There is research looking at, is there a new lake-wide treatment that people just haven't thought of yet? But most of these species, that's one of their issues, is that there is not a way to just take care of them."