Mauthe Lake

Mauthe Lake sits at a C on the grading scale — not impaired, not pristine, with summer measurements that vary year to year. clarity and phosphorus rate similarly, so there is no obvious single lever to pull on watershed management.

A TSI in the eutrophic range signals a lake doing what nutrient-loaded waters do — supporting an active algal community at the cost of clear water. The lake bottoms out at 23 ft — a moderate depth that supports a warm-water fishery without the year-round cold refuge a deeper basin provides. Mauthe Lake is small — 70 acres alongside partial shoreline records — which makes it sensitive to even modest changes in watershed runoff or recreational pressure. Within Fond du Lac County's 10 graded lakes, Mauthe Lake ranks 7 — below the local median, though not at the bottom.

Zebra mussels have been documented at Mauthe Lake, which alters the filter-feeding balance and can paradoxically increase water clarity while disrupting the food web. Walleye are documented at Mauthe Lake, one of 4 fish species on record for the lake. 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.