The drawdown of the Sartell Pool of the Mississippi River and Little Rock Lake began at midnight on Aug. 1 and was completed at 6:20 a.m. on Aug. 2, when the water level at the Sartell Dam had dropped three feet.
According to the Minnesota Department of Natural Resources, the goal of the project is to improve water quality, stabilize eroding shorelines and increase habitat for fish and other wildlife on Little Rock Lake in Benton County north of St. Cloud.
“The water level on the lake is dropping more slowly than the river,” said Eric Altena, DNR fisheries supervisor in Little Falls. “Water flowing from the lake to the river is constricted by a narrow channel.”
Altena said the water level on Little Rock Lake was still more than six inches higher than the target level on Aug. 8.
The flow through the channel is scouring away much of the silt and other sediments that had settled on the bottom for more than 100 years. The combination of current and lower water even uncovered a submerged snowmobile that is still being investigated.
On Aug. 4, DNR employees and volunteers finished planting approximately eight acres of emergent plants in various locations around the lake. The crews used augers to drill holes in the drying mud flats then planted bulbs.
“Aquatic vegetation provides fish habitat and processes the excess nutrients that lead to algae blooms,” Altena said. “One pound of phosphorus can produce 500 pounds of algae.”
Voluntary programs on the watershed that feeds Little Rock Lake have already reduced the phosphorus load in tributary streams by 2,500 pounds per year.
When the water level begins to rise in mid-September, water from the Mississippi River will begin to flow into Little Rock Lake.
“Water clarity on the river is about three feet, compared to a foot or less on the lake,” Altena said. “We expect to see an immediate visibility improvement, though the rising water level on the lake will lag about a week behind the river.”
A no-wake zone will remain in effect on the Sartell Pool and Little Rock Lake until Sept. 15.