City Millpond

The LakeGrade rubric puts City Millpond at a C: clarity readings still being added, 38 µg/L of phosphorus, and a TSI of 57 signal an intermediate trophic state. 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.

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. At 236 ft of maximum depth, City Millpond stratifies reliably through the summer — the hypolimnion stays cooler and clearer than the surface layer suggests. With 7,920 acres of surface and partial shoreline records, City Millpond is a large water by Wisconsin standards — recreational pressure is spread across a long shoreline. Within Green Lake County's 13 graded lakes, City Millpond ranks 9 — below the local median, though not at the bottom.

Zebra mussel presence at City Millpond means the lake's clarity numbers carry an asterisk — filtered water is not the same as nutrient-poor water. Walleye are documented at City Millpond, one of 7 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.