Southwest Minneapolis’ most popular lakes for recreation earned high marks for water quality on Minnehaha Creek Watershed District’s 2012 Lake Grades report released May 9.
Lake Calhoun earned an A and Lake Harriet earned an A- from the watershed district, grades that indicate the lakes are generally healthy and have clear water throughout the summer. Cedar Lake, the only other lake in the Chain of Lakes with public beaches, scored a B+.
The grades were based on water samples collected last year between May and September and consider three factors: water clarity, phosphorous levels and algae abundance. Lakes that scored a C on the report — including Lake of the Isles — are considered to have average water quality for the 181-square-mile watershed district.
The Minneapolis Park and Recreation Board conducts the sampling for lakes in Minneapolis, and Rachael Crabb, a Park Board water quality specialist, said she was “pretty happy” with this year’s grades.
“I think our lakes are doing great for urban lakes that are challenged with storm water,” Crabb said.
That challenge is tougher for tiny Brownie Lake, the northernmost link on the Chain of Lakes. It earned a C- on the report, a result Crabb said had to do with the lake’s outsized watershed.
She said the Southwest Calhoun Wetland, an artificial storm water pond, is one example of a structure that helps protect water quality by filtering storm water before it enters Lake Calhoun. It captures some of the sediment that can lower water clarity and the vegetation that increases phosphorous levels and contributes to summer algae blooms.
Spring street sweeping and residential rain gardens also help protect the health of the city’s lakes, Crabb added.
None of the lakes in the Chain of Lakes shifted more than half a letter grade from the previous Lake Grades report, and for the most part water quality for those lakes has varied little over the past decade. Still, an effort is underway to examine long-term water-quality trends in the district.
Kelly Dooley, a watershed district water quality specialist, said district staff was sorting through sampling data that goes as far back as the 1970s for some lakes in the district. The results of the statistical analysis are expected in June or July, Dooley said.
Click here to read more about the 2012 Lake Grades report on the Minnehaha Creek Watershed District website.