By Kirsti Marohn

MPR News/90.1 FM

Six years ago, Aaron Trompeter jumped at what he thought was a great deal on lakeshore property.

He bought his house on Little Rock Lake in early June. But by late summer, entire sections of the lake were coated with bright green algae.

“I don’t swim off my dock,” Trompeter said during a boat ride last week. “I’ll go into the main lake and I’ll swim this early in the year. But not in August. In August, it’s stinky.”

This shallow reservoir of the Mississippi River just north of St. Cloud was once a popular fishing and recreation destination. Today, it’s a lot quieter.

Trompeter said Little Rock Lake “should be St. Cloud’s Minnetonka,” but the poor water quality keeps people away.

For decades, the lake was overloaded with phosphorus and nitrogen from a large watershed that drains a lot of farmland. Those nutrients have fueled the growth of algae “so thick that you actually could hear it on the bottom of an aluminum boat passing over it,” said Eric Altena, the Minnesota Department of Natural Resources’ fisheries manager in Little Falls.

The result: Little Rock Lake has almost no natural plant growth. Plants are an important element of a lake’s health — and they keep the shoreline from eroding, Altena said. He said Little Rock Lake is among the state’s worst, when it comes to water quality.

For years, residents and experts have debated ways to reduce nutrients and improve the clarity of Little Rock Lake. Most efforts have focused on working with farmers to reduce fertilizer runoff and fixing failing septic systems.

Now, they’re ready to try a more dramatic approach.

On Aug. 1, the Department of Natural Resources plans to drop the lake level by 3 feet over three days by opening the gates of the Sartell dam downstream on the Mississippi River. The drawdown is expected to expose hundreds of feet of mud flats in the shallower parts of the lake.

If all goes as planned, plants will quickly start to grow in the rich sediment of the lake bottom, using up the excess phosphorus and nitrogen nutrients. Volunteers, including a troop of Boy Scouts, will help by planting native plants in the mud beds.

After six weeks, the DNR will raise the water back to its typical levels. And by next summer, Altena expects to see significant improvement in Little Rock Lake’s water quality. He estimates the lake’s transparency should increase at least 50 percent.

“Considering that water clarity’s usually less than a foot, we’ll be doing pretty good,” he said.

Lake drawdowns aren’t a new concept in Minnesota. They have been tried since the early 1970s on several other lakes, including Pelican in Wright County and Swan in Nicollet County.

Most drawdowns have targeted shallow lakes with the goal of eliminating carp or improving waterfowl habitat, said Nicole Hansel-Welch, the DNR’s shallow lakes program supervisor.

“We don’t purport that this is a magic bullet,” she said. “It’s one of the tools in the toolbox.”

Lake drawdowns have received a financial boost from the Legacy amendment — the constitutional amendment Minnesota voters approved in 2008 that dedicates sales tax money to the outdoors, clean water and the arts.

The Little Rock Lake drawdown received a Legacy grant of $198,000, which will pay the company that owns the Sartell dam for lost electricity production. Community donations and the Little Rock Lake Association will cover the remainder of the $235,000 cost.