Mule Lake

Mule Lake sits at the top of the Minnesota PCA grading rubric with an A, a mark reached by the cleanest lakes in Minnesota. Clarity, phosphorus, and chlorophyll-a all rate similarly, so there is no obvious single lever to pull on watershed management.

The lake's low TSI puts it in oligotrophic territory — the cleanest of the four trophic classes, but also the most vulnerable to nutrient-driven shifts. Mule Lake reaches 31 ft at its deepest point — typical for Minnesota mid-sized lakes, with seasonal stratification but limited cold-water refuge. At 53 acres, Mule Lake sits below the Minnesota median: a small water where shoreline activity has an outsized effect on water quality. Among the 97 graded lakes in Otter Tail County, Mule Lake ranks 23 — in the top quartile locally.

No invasive species are currently listed at Mule Lake — the lake remains off the Minnesota infested-waters roster. The state fisheries records do not list documented species for Mule Lake, which usually reflects a lack of formal fisheries survey work rather than an empty lake. The lake lacks a documented public access point, so visitor use is limited. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.