Lac Courte Oreilles Lake

Lac Courte Oreilles Lake sits at the top of the Wisconsin DNR grading rubric with an A, a mark reached by the cleanest lakes in Wisconsin. 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. Lac Courte Oreilles Lake is unusually deep for Wisconsin at 90 ft, which buffers the lake against summer warming and helps the deep water stay oxygenated. With 5,139 acres of surface and partial shoreline records, Lac Courte Oreilles Lake is a large water by Wisconsin standards — recreational pressure is spread across a long shoreline. Within Sawyer County's 50 graded waters, Lac Courte Oreilles Lake sits at rank 8, near the top of the local distribution.

Lac Courte Oreilles Lake carries an invasive watermilfoil record — boat-launch decontamination and shoreline care matter more here than at uninfested lakes. The fishery includes walleye among the lake's 6 documented species — a notable draw for Wisconsin anglers. The grade is supported by multiple sampling years from the Wisconsin DNR Citizen Lake Monitoring Network, giving the letter a reasonably stable foundation.