Loon Lake

Loon Lake grades an F: water clarity, phosphorus, and chlorophyll-a all rate poorly, placing it among the most stressed lakes monitored in Minnesota. Sub-grades cluster within a single letter of each other, which usually means the lake is in stable trophic balance rather than fighting one specific stressor.

Eutrophic conditions are the baseline here: clarity drops noticeably in late summer, and dissolved oxygen near the bottom can become a concern. Loon Lake is a shallow lake at 7 ft maximum depth, which means it warms quickly, mixes constantly, and amplifies nutrient inputs. At 809 acres, Loon Lake fits the Minnesota median for monitored lakes, with 5.3 miles of shoreline. Loon Lake ranks 9 of 9 in Blue Earth County — at the lower end of the locally monitored distribution.

No invasive species are currently listed at Loon Lake — the lake remains off the Minnesota infested-waters roster. The fishery includes walleye alongside the lake's other 13 documented species — a notable draw for Minnesota anglers. 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.