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 and phosphorus 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 among the lake's 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.