Cooper Lake

On the LakeGrade rubric, Cooper Lake pulls an A: clarity at 17.1 ft and 13 µg/L of phosphorus put it in the top bracket for Minnesota. The three sub-grades — clarity, phosphorus, and chlorophyll-a — track close together, so no single parameter is dragging the average.

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. At 70 ft of maximum depth, Cooper Lake stratifies reliably through the summer — the hypolimnion stays cooler and clearer than the surface layer suggests. Cooper Lake covers 133 acres alongside 3.0 miles of shoreline — a mid-sized water that supports a working fishery without being so large that conditions diverge between basins. Among the 133 graded lakes in Cass County, Cooper Lake ranks 33 — in the top quartile locally.

Cooper Lake has no invasive species recorded in Minnesota state databases as of 2024, though prevention practices still apply at all access points. The fishery is bass-led, with 12 documented species across the lake's records. No formal public access is documented at Cooper 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.