Prong Lake

Prong 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. Prong Lake is unusually deep for Wisconsin at 50 ft, which buffers the lake against summer warming and helps the deep water stay oxygenated. Prong Lake is small — 31 acres alongside partial shoreline records — which makes it sensitive to even modest changes in watershed runoff or recreational pressure. Prong Lake sits at rank 140 of 202 in Vilas County, in the lower half of the local distribution.

Prong Lake has no invasive species recorded in Wisconsin state databases as of 2024, though prevention practices still apply at all access points. Bass fishing is part of the appeal: the species list runs to 2, anchored by largemouth and/or smallmouth bass. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.