Water Clarity Treatments Begin on Crystal Lake in Robbinsdale
The city of Robbinsdale and the Shingle Creek Watershed Commission started work to improve water clarity on Crystal Lake on Thursday.
Crews applied alum, a chemical used to high phosphorus levels, to the lake. But it was a lighter treatment than expected.
“The plan was to do it all today, but the lake’s pH is not in the right range,” said Marta Roser, Robbinsdale’s water resources specialist. “We’ve had a very warm week. We’ve had some algae blooms early on and that might’ve affected the pH of the lake.”
Roser calls the phosphorus “legacy phosphorus.”
“A lot of phosphorus has come into the lake and there’s no natural outlet so everything that comes in, stays,” Roser explained. “Then it is released from the sediment. What the alum does is catches everything in the water column and brings it down and forms a barrier to keep any more phosphorus from getting out.”
Roser says the alum acts like a nice cap over the sediment.
The alum treatment is still safe for boaters and wildlife in the water. Crews plan the full treatment in the fall.
Carp Also a Problem
The city says the lake does not meet state water quality standards for nutrients. The city has implemented stormwater best management practices as well as treating lake water during the summer at the facility in Lakeview Terrace Park.
There’s also a problem with carp. The Shingle Creek Watershed Commission worked with city staff to determine the number of carp in the lake and found out there’s too many. The bottom-feeding, non-native fish can stir up sediment, uproot vegetation and remove the habitat for native fish species. Crews plan to start work on removing carp after the alum treatment is complete.
The cost of the project will be funded by the Shingle Creek Watershed Commission through a federal grant and commission funds.