For years, the water in Little Rock Lake has turned green by midsummer, choked with algae that makes Benton County’s largest lake look from the air like a golf course fairway.
A blue-green algae bloom in 2007 was so bad that the Minnesota Pollution Control Agency conducted tests and found algal toxins considered a health risk.
Now, with the help of a hydroelectric dam, some native plants and 500 Boy Scouts, there might be hope.
On Aug. 1, the Eagle Creek Renewable Energy will let enough water pass through its dam in Sartell, Minn., to allow for a 3-foot drawdown of lake levels. Boy Scouts and others carrying thousands of dollars worth of native bulrush plants will seed the shoreline over two weekends in August.
By next summer, those plants should suck up phosphorus and other nutrients as they take root in the lake bed, said Eric Altena, a DNR fisheries manager based in Little Falls, Minn. The plants could dramatically improve water quality, he said. “We’re looking at the lowest cost, most effective option,” Altena said.
Drawdowns have been used in lakes and portions of the Mississippi River to restore water quality, help improve fish and wildlife and fight erosion. The plan has been years in the making and wasn’t too popular when the DNR suggested it to the Little Rock Lake Association, Altena said. “They almost ran me out of the meeting,” he said.
Today, association president Kellie Gallagher said she wholeheartedly endorses the drawdown. Numerous people have stepped forward to support it, starting with area farmers, she said.
The lake’s disastrous algae growth was stimulated largely by runoff from nearby farms that loaded the lake with nitrates and phosphorus. The Benton County Soil and Water Conservation District worked with local farmers for the past five years, writing more than 70 individual management plans for farms within the Little Rock Lake watershed.
Each of those farms took measures to reduce the fertilizer and soil seeping into the lake, including larger buffer zones, cover crops or the construction of expensive feedlots — concrete pads at feeding areas that make it easier to manage cow manure and prevent it from running into local waterways.
Nearly nine in 10 farmers in the region took steps to help improve the lake’s water quality, Gallagher said. “Our farmers are doing a great job.”
Those efforts reduced nitrates, phosphorus, soil and fecal matter contamination pouring into the lake from the three streams that flow into it, Gallagher said.
Altena estimates that farmers cut phosphorus levels flowing into the lake by about 2,500 pounds a year, or enough to grow almost a million pounds of algae. The lake had as much as 600 parts per billion of phosphorus at its peak in 2007, he said. It’s down to 124 parts now, and Altena hopes it will fall below 90 after the effects of the drawdown.
Little Rock Lake was created in 1911 when builders finished the Sartell dam some 5 miles downstream. The 1,400-acre lake has an average depth of about 8 feet and is 23 feet at its deepest. The lake empties into the Mississippi River at its southern tip.
The dam in Sartell will lose about $235,000 from lost power generation during the six-week drawdown. A grant from the Minnesota Board of Soil and Water Resources will cover much of that cost, and Eagle Creek Renewable Energy agreed to cover some of the losses, leaving a gap of several thousand dollars.
There are more costs to cover, though, like feeding those Boy Scouts. “The whole community is just stepping up,” Gallagher said.