Ossawinnamakee Lake

Ossawinnamakee 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. At 63 ft of maximum depth, Ossawinnamakee Lake stratifies reliably through the summer — the hypolimnion stays cooler and clearer than the surface layer suggests. Ossawinnamakee Lake covers 711 acres alongside 13.3 miles of shoreline — a mid-sized water that supports a working fishery without being so large that conditions diverge between basins. Among the 120 graded lakes in Crow Wing County, Ossawinnamakee Lake ranks 5 — in the top quartile locally.

Zebra mussels have been documented at Ossawinnamakee Lake, which alters the filter-feeding balance and can paradoxically increase water clarity while disrupting the food web. The fishery includes walleye alongside the lake's other 18 documented species — a notable draw for Minnesota anglers. Public access is available — the lake is on the Minnesota PCA public-access list. Ice-out has been logged at Ossawinnamakee Lake more than two dozen times, putting the median around Apr 17 — a useful baseline for tracking climate trends. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.