Rock Lake

Rock Lake earns an A — water clarity, phosphorus, and chlorophyll-a all rate among the best monitored waters in Jefferson County. 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. The lake's 60 ft maximum depth is in the upper tier for Wisconsin — deep enough for cold-water fish to find refuge in summer. Rock Lake covers 1,365 acres alongside partial shoreline records, large enough that conditions can vary meaningfully between bays. Rock Lake ranks 1 of 8 in Jefferson County, putting it in the upper tier of locally monitored lakes.

Zebra mussels have been documented at Rock 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 5 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.