Delavan Lake

Delavan Lake carries a solid B grade — strong on most parameters, with measurements that hold up well across the summer season. Clarity, phosphorus, and chlorophyll-a all rate similarly, so there is no obvious single lever to pull on watershed management.

A TSI near 48 places Delavan Lake in the mesotrophic band — moderate productivity, with seasonal swings between clearer spring water and richer late-summer conditions. 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. Within Walworth County's 34 graded lakes, Delavan Lake ranks 24 — 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. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.