Loon Lake

Loon Lake earns a D — measurements through 2023 show persistent nutrient pressure that limits clarity through the summer.

At a TSI of 57, Loon Lake reads as eutrophic — nutrient-rich enough that summer algal growth and reduced clarity are expected, not unusual. A maximum depth of 21 ft puts Loon Lake in the middle of Minnesota's depth distribution. At 34 acres, Loon Lake sits below the Minnesota median: a small water where shoreline activity has an outsized effect on water quality. 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. The lake's fish records list 3 species — a varied community without one dominant gamefish. 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.