Green Lake

Green Lake earns an A — water clarity, phosphorus, and chlorophyll-a all rate among the best monitored waters in Walworth County. 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 57 ft of maximum depth, Green Lake stratifies reliably through the summer — the hypolimnion stays cooler and clearer than the surface layer suggests. Green Lake covers 311 acres alongside partial shoreline records — a mid-sized water that supports a working fishery without being so large that conditions diverge between basins. Within Walworth County's 34 graded waters, Green Lake sits at rank 3, near the top of the local distribution.

Zebra mussels have been documented at Green 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 4 documented species — a notable draw for Wisconsin anglers. Public access is available — the lake is on the Wisconsin DNR public-access list. Monitoring depth is thin here: the LakeGrade rubric is applied to a small number of sample years, and the grade will be revised as more data accumulates.