North Lake

North Lake sits at the top of the Wisconsin DNR grading rubric with an A, a mark reached by the cleanest lakes in Wisconsin. The three sub-grades — clarity, phosphorus, and chlorophyll-a — track close together, so no single parameter is dragging the average.

A TSI value of 37 puts North Lake in the oligotrophic range, where biological productivity stays low and the water column remains clear. North Lake is unusually deep for Wisconsin at 78 ft, which buffers the lake against summer warming and helps the deep water stay oxygenated. North Lake covers 440 acres alongside partial shoreline records — a mid-sized water that supports a working fishery without being so large that conditions diverge between basins. Among the 48 graded lakes in Waukesha County, North Lake sits at rank 15, above the county median.

Zebra mussel presence at North Lake means the lake's clarity numbers carry an asterisk — filtered water is not the same as nutrient-poor water. Walleye are documented at North Lake, one of 5 fish species on record for the lake. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.