Ryan Lake and Lower Twin Lake also are part of Robbinsdale’s efforts.
On almost any day, in almost every season, the parks, sidewalks, bike paths and docks near Robbinsdale’s Crystal Lake are lively with walkers, runners, bicyclists, anglers, bird-watchers, children and others enjoying the picturesque setting in the heart of a busy urban area.
But on summer days, the little lake itself can be a turnoff. The water is murky at best, pea-soup green at worst.
In recent years, Robbinsdale has been making efforts to clean up three of its lakes — Crystal, Ryan and Lower Twin lakes. Top priority is Crystal Lake, part of the Shingle Creek Watershed, which ultimately flows into the Mississippi River.
In 2002, Crystal Lake was placed on the state’s impaired-waters list due to its unhealthy excess of nutrients. To get off that list, it must reduce its phosphorus intake, according to the Minnesota Pollution Control Agency.
When a lake has too much phosphorus, it takes on a pea-soup appearance due to algae blooms, said Barb Peichel of the MPCA. That makes the lake unsuitable for swimming.
To address the problem, Crystal Lake has been made part of a Total Maximum Daily Load project, according to Miranda Nichols, the MPCA’s impaired-waters list coordinator. In the case of Crystal Lake, the goal is to reduce the amount of phosphorus by 72 percent.
Excess amounts of phosphorus get into the lake via untreated stormwater. When residents do not remove leaves and grass clippings from the street, excess nutrients caused by decay and chemical runoff end up in the lake and lead to algae blooms, Peichel said.
City representatives and various agencies came together to determine a strategy they hope will help make the lake swimmable again someday.
The Crystal Lake Flocculation Plant, housed in a large tank on the south side of the lake, was installed in 2012 as part of that strategy, according to City Manager Marcia Glick.
The plant, which operates from May to November, draws in water from the lake, which then mixes with the chemical alum to bind with the phosphorus, said Richard McCoy, Robbinsdale’s city engineer and public works director.
The binded material, called floc, is discharged into the sanitary sewer system with the approval of the Metropolitan Council, McCoy said. The clean water goes back into the lake or ponds.
Last year, in its first full year of operation, the plant removed 200 pounds of phosphorus from Crystal Lake, he said.
The cost of building the plant was approximately $1.2 million, with funds coming from Hennepin County, Shingle Creek Watershed Commission and the city of Robbinsdale, McCoy said. To run the plant each year will cost approximately $90,000.
Other efforts to clean up the lake include the construction of rain gardens, more thorough street sweeping, pollutant traps in storm sewer systems and the statewide phosphorus-free fertilizer ordinance, among others, McCoy said.
“With all the different projects that have been implemented, we are hopeful that the conditions in the lake will improve,” McCoy said. “However, the mechanics of lake ecology [are] complex, making it difficult to predict how long it might take to see improved water quality in the lake.”
Ryan and Lower Twin lakes are part of a chain of lakes that also includes Upper Twin and Middle Twin lakes.
Projects to improve Lower Twin Lake include the construction of water quality ponds and rain gardens, street sweeping, and other projects that can help prevent phosphorus from seeping into the lakes, McCoy said. And improvements made to Lower Twin Lake are expected to improve the water quality in Ryan Lake, he said.