Green Lake

On the LakeGrade scale Green Lake grades a B, with clarity at 13.0 ft and phosphorus readings still being added placing it above the Wisconsin median. Clarity, phosphorus, and chlorophyll-a all rate similarly, so there is no obvious single lever to pull on watershed management.

Mesotrophic conditions dominate at Green Lake: enough nutrients for a healthy fishery, not so much that algal blooms become a chronic problem. The lake's 236 ft maximum depth is in the upper tier for Wisconsin — deep enough for cold-water fish to find refuge in summer. With 7,920 acres of surface and partial shoreline records, Green Lake is a large water by Wisconsin standards — recreational pressure is spread across a long shoreline. Among the 13 graded lakes in Green Lake County, Green Lake ranks 3 — in the top quartile locally.

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. The fishery includes walleye alongside the lake's other 7 documented species — a notable draw for Wisconsin anglers. 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.