Marl Lake

Marl Lake earns an A — every scored parameter (clarity and phosphorus) rates among the best monitored waters in Waupaca County. The two scored sub-grades — clarity and phosphorus — track close together, so neither one is dragging the average down.

A TSI value of 38 puts Marl Lake in the oligotrophic range, where biological productivity stays low and the water column remains clear. At 59 ft of maximum depth, Marl Lake stratifies reliably through the summer — the hypolimnion stays cooler and clearer than the surface layer suggests. At 14 acres, Marl Lake sits below the Wisconsin median: a small water where shoreline activity has an outsized effect on water quality. Within Waupaca County's 25 graded waters, Marl Lake sits at rank 6, near the top of the local distribution.

Zebra mussels have been documented at Marl Lake, which alters the filter-feeding balance and can paradoxically increase water clarity while disrupting the food web. The fishery includes walleye among the lake's 5 documented species — a notable draw for Wisconsin anglers. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.