Lake Butte des Morts

Lake Butte des Morts sits at a C on the grading scale — not impaired, not pristine, with summer measurements that vary year to year. 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.

A TSI near 48 places Lake Butte des Morts in the mesotrophic band — moderate productivity, with seasonal swings between clearer spring water and richer late-summer conditions. A maximum depth of just 9 ft means sediment-bound phosphorus releases back into the water column whenever wind stirs the bottom — a classic shallow-lake dynamic. At 8,581 acres, Lake Butte des Morts is one of the larger lakes in Winnebago County, with partial shoreline records supporting multiple distinct use patterns. Within Winnebago County's 5 graded lakes, Lake Butte des Morts ranks 3 — below the local median, though not at the bottom.

Zebra mussels have been documented at Lake Butte des Morts, 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 8 documented species — a notable draw for Wisconsin anglers. 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.