Green Lake

Green Lake sits at the top of the Wisconsin DNR grading rubric with an A, a mark reached by the cleanest lakes in Wisconsin. Clarity, phosphorus, and chlorophyll-a all rate similarly, so there is no obvious single lever to pull on watershed management.

A TSI value of 36 puts Green Lake in the oligotrophic range, where biological productivity stays low and the water column remains clear. A maximum depth of 37 ft puts Green Lake in the middle of Wisconsin's depth distribution. The lake is compact at 70 acres, with partial shoreline records and little volume to buffer nutrient inputs. Among the 15 graded lakes in Washington County, Green Lake ranks 1 — in the top quartile locally.

Eurasian watermilfoil has been documented at Green Lake, requiring shoreline management to keep dense mats from crowding native vegetation. The fishery includes walleye alongside the lake's other 4 documented species — a notable draw for Wisconsin anglers. Public access is available — the lake is on the Wisconsin DNR public-access list. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.