Upper Nemahbin Lake

Upper Nemahbin Lake earns an A — water clarity, phosphorus, and chlorophyll-a all rate among the best monitored waters in Waukesha County. 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.

Mesotrophic conditions dominate at Upper Nemahbin Lake: enough nutrients for a healthy fishery, not so much that algal blooms become a chronic problem. At 60 ft of maximum depth, Upper Nemahbin Lake stratifies reliably through the summer — the hypolimnion stays cooler and clearer than the surface layer suggests. At 277 acres, Upper Nemahbin Lake fits the Wisconsin median for monitored lakes, with partial shoreline records. Upper Nemahbin Lake ranks 18 of 45 in Waukesha County — solidly in the upper half of the local distribution.

Zebra mussels have been documented at Upper Nemahbin Lake, which alters the filter-feeding balance and can paradoxically increase water clarity while disrupting the food web. Walleye are documented at Upper Nemahbin Lake, one of 5 fish species on record for the lake. Public access is available — the lake is on the Wisconsin DNR public-access list. 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.