Onagon Lake

Onagon Lake earns a D — measurements through 2024 show persistent nutrient pressure that limits clarity through the summer. Clarity, phosphorus, and chlorophyll-a all rate similarly, so there is no obvious single lever to pull on watershed management.

Eutrophic conditions are the baseline here: clarity drops noticeably in late summer, and dissolved oxygen near the bottom can become a concern. Onagon Lake reaches 15 ft at its deepest point — typical for Minnesota mid-sized lakes, with seasonal stratification but limited cold-water refuge. The lake is compact at 31 acres, with 1.4 miles of shoreline and little volume to buffer nutrient inputs. Within the 128 graded lakes of Cook County, Onagon Lake sits at rank 102, near the bottom of the county list.

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