Green Lake

The LakeGrade rubric puts Green Lake at a C: clarity at 11.5 ft, 67 µg/L of phosphorus, and a TSI of 53 signal an intermediate trophic state. Phosphorus is the parameter holding the grade back — runoff from the surrounding watershed appears to keep nutrient levels elevated through the summer.

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, Green Lake stratifies reliably through the summer — the hypolimnion stays cooler and clearer than the surface layer suggests. 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. Green Lake ranks 6 of 13 in Green Lake County — solidly in the upper half of the local distribution.

Green Lake is on the Wisconsin infested-waters list for zebra mussels — boaters should follow clean-drain-dry protocols when moving gear to or from the lake. The fishery includes walleye among the lake's 7 documented species — a notable draw for Wisconsin anglers. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.