Marl Lake

Marl Lake earns an A — water clarity, phosphorus, and chlorophyll-a all rate among the best monitored waters in Waupaca County. The three sub-grades — clarity, phosphorus, and chlorophyll-a — track close together, so no single parameter is dragging the average.

A TSI value of 30 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. Among the 27 graded lakes in Waupaca County, Marl Lake sits at rank 12, above the county median.

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 alongside the lake's other 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.