Serpent Lake in Crosby is home to fishing tournaments, boat races, and just about anyone trying to enjoy a summer day. However, the water clarity in the lake had been decreasing, but new efforts have reversed that trend and Serpent Lake is as clear as it’s been since 1991.

“Our biggest factor was phosphorous coming into the lake,” Terry Tichenor, Serpent Lake Association President, said.

Phosphorous is an element that algae and other plants love to feed on. When phosphorous gets in a lake, algae grow, and the water quality and clarity decreases. Most of Deerwood’s storm water was running right into Serpent Lake full of phosphorous.

“As the water runs down the street it picks up debris, it picks up particles from the ground, and that all has […] phosphorous.” Melissa Barrick, Crow Wing Soil & Water Conservation District Manager, said.

To combat this, the Crow Wing Soil & Water Conservation District dug basins to control the water and filter the phosphorous.

“It’s a system that collects all of this runoff in the city of Deerwood, runs it through these settling ponds and filters,” Tichenor said. “It uses iron filings to extract the phosphorous from the water, and allows the water to percolate fairly clarified into the lake.”

Another reason why Serpent Lake was being flooded with phosphorous is because the city of Deerwood was using a connecting lake as a discharge site for their wastewater. Barrick and her team performed an Alum Treatment to help remove the phosphorous before it reaches Serpent Lake.

“An Alum Treatment is a chemical you put in lakes to bind the phosphorous to the bottom of the lake,” Barrick said.

Their efforts have removed 78 pounds of phosphorous, and stopped over 20 tons of algae from potentially growing.

The filtration system has not only improved the water clarity of Serpent Lake, but it has also prevented homes that are right on the water from potential flooding.

“The 100-year rain seemed to come every five years,” Michael Aulie, Deerwood Mayor, said. “It was major flooding down here, pretty much everything was underwater.”

Thanks to the basins, the flooding has decreased, and Serpent Lake has a water clarity of 18 feet, the best it’s been since 1991.

The Serpent Lake Association measures water clarity on a monthly basis to ensure phosphorous is not re-entering the lake.

By — Anthony Scott