Delavan Lake

Delavan Lake carries a solid B grade — strong on most parameters, with measurements that hold up well across the summer season. Sub-grades cluster within a single letter of each other, which usually means the lake is in stable trophic balance rather than fighting one specific stressor.

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. With 1,906 acres of surface and partial shoreline records, Delavan Lake is a large water by Wisconsin standards — recreational pressure is spread across a long shoreline. Among the 35 graded lakes in Walworth County, Delavan Lake sits at rank 16, above the county median.

Zebra mussel presence at Delavan Lake means the lake's clarity numbers carry an asterisk — filtered water is not the same as nutrient-poor water. Walleye are documented at Delavan Lake, one of 6 fish species on record for the lake. 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.