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.

Eutrophic conditions are the baseline here: clarity drops noticeably in late summer, and dissolved oxygen near the bottom can become a concern. The lake's 52 ft maximum depth is in the upper tier for Wisconsin — deep enough for cold-water fish to find refuge in summer. 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. Within Walworth County's 34 graded lakes, Delavan Lake ranks 22 — below the local median, though not at the bottom.

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.