RICE — The Minnesota DNR held an informational meeting here this week to discuss the drawdown of the Sartell Pool on the Mississippi River.
The pool is north of St. Cloud and is connected to Little Rock Lake, a 1,300-acre reservoir that was impounded by the construction of the Sartell Dam in 1907.
“Water quality in the lake is poor,” said Eric Altena, Minnesota DNR area fisheries supervisor in Little Falls. “Water clarity is almost nonexistent and there is no emergent vegetation. That makes poor habitat for fish, migratory birds and other wildlife.”
The drawdown is scheduled to begin on Aug. 1, when the water level at the Sartell Dam will be lowered just over an inch per hour for 30 hours.
“The goal is to lower the water three feet,” Altena added. “That will expose roughly 700 acres of mud flats on Little Rock Lake to sun and air. That exposure will allow the DNR and members of the Little Rock Lake Association to plant aquatic and terrestrial vegetation to improve water quality and stabilize the shoreline.”
The poor water quality in the lake is caused in part by high phosphorus concentrations that fuel algae blooms every year. Aquatic vegetation — especially emergent varieties like cattails and bullrushes — use those excess nutrients to grow.
“Every pound of phosphorus in the lake has the potential to produce 500 pounds of algae,” Altena said. “We need weeds to keep the water clear, but weeds need clear water to grow. We think this drawdown will flip the reservoir to a clear and stable condition.”
Altena said it’s impossible to pinpoint exact outcomes, but he conservatively estimates the $200,000 project will result in a 30% reduction in phosphorus in the lake and a 50% increase in water clarity.
Low water levels will be maintained until Sep. 14, for a total of six weeks. Altena said that a no-wake zone will be in effect during that period on the Sartell Pool and Little Rock Lake. Motorized vehicles also are prohibited below the normal high-water line.
For more information, visit the DNR project page at https://www.dnr.state.mn.us/areas/fisheries/littlefalls/drawdown.html.