Onagon Lake

Onagon Lake earns a D — measurements through 2024 show persistent nutrient pressure that limits clarity through the summer.

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 15 ft — a moderate depth that supports a warm-water fishery without the year-round cold refuge a deeper basin provides. Onagon Lake is small — 31 acres alongside 1.4 miles of shoreline — which makes it sensitive to even modest changes in watershed runoff or recreational pressure. 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. 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.