Delavan Lake

On the LakeGrade scale Delavan Lake grades a B, with clarity at 9.3 ft and 27 µg/L of phosphorus placing it above the Wisconsin median. Clarity, phosphorus, and chlorophyll-a all 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. Delavan Lake is unusually deep for Wisconsin at 52 ft, which buffers the lake against summer warming and helps the deep water stay oxygenated. At 1,906 acres, Delavan Lake is one of the larger lakes in Walworth County, with partial shoreline records supporting multiple distinct use patterns. Among the 35 graded lakes in Walworth County, Delavan Lake sits at rank 15, above the county median.

Zebra mussels have been documented at Delavan 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 6 documented species — a notable draw for Wisconsin anglers. A documented public access point at Delavan Lake makes the lake usable for shore fishing, paddle craft, and trailered boats. 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.