Loon Lake

Loon Lake earns a D — measurements through 2023 show persistent nutrient pressure that limits clarity through the summer. The three sub-grades — clarity, phosphorus, and chlorophyll-a — track close together, so no single parameter is dragging the average.

A TSI in the eutrophic range signals a lake doing what nutrient-loaded waters do — supporting an active algal community at the cost of clear water. The lake bottoms out at 21 ft — a moderate depth that supports a warm-water fishery without the year-round cold refuge a deeper basin provides. The lake is compact at 34 acres, with 1.1 miles of shoreline and little volume to buffer nutrient inputs. Within the 53 graded lakes of Aitkin County, Loon Lake sits at rank 48, near the bottom of the county list.

No invasive species are currently listed at Loon Lake — the lake remains off the Minnesota infested-waters roster. 3 fish species are documented at Loon Lake, a mixed warm-water community typical for Minnesota lakes of this size. Public access is available — the lake is on the Minnesota PCA public-access list. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.