Green Lake

On the LakeGrade scale Green Lake grades a B, with clarity at 14.1 ft and 32 µg/L of phosphorus placing it above the Wisconsin median. The three sub-grades — clarity, phosphorus, and chlorophyll-a — track close together, so no single parameter is dragging the average.

Mesotrophic conditions dominate at Green Lake: enough nutrients for a healthy fishery, not so much that algal blooms become a chronic problem. Green Lake is unusually deep for Wisconsin at 236 ft, which buffers the lake against summer warming and helps the deep water stay oxygenated. At 7,920 acres, Green Lake is one of the larger lakes in Green Lake County, with partial shoreline records supporting multiple distinct use patterns. Among the 13 graded lakes in Green Lake County, Green Lake sits at rank 5, above the county median.

Zebra mussels have been documented at Green Lake, which alters the filter-feeding balance and can paradoxically increase water clarity while disrupting the food web. Walleye are documented at Green Lake, one of 7 fish species on record for the lake. A documented public access point at Green Lake makes the lake usable for shore fishing, paddle craft, and trailered boats. 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.