Rock Lake

Rock Lake earns an A — every scored parameter (clarity and phosphorus) rates among the best monitored waters in Jefferson County. clarity and phosphorus rate similarly, so there is no obvious single lever to pull on watershed management.

The lake sits in the mesotrophic zone — the band where most well-managed Wisconsin lakes fall. 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 among the lake's 5 documented species — a notable draw for Wisconsin anglers. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.