Big Lake

Big 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 38 puts Big Lake in the oligotrophic range, where biological productivity stays low and the water column remains clear. The lake bottoms out at 24 ft — a moderate depth that supports a warm-water fishery without the year-round cold refuge a deeper basin provides. At 245 acres, Big Lake fits the Wisconsin median for monitored lakes, with partial shoreline records. Big Lake ranks 30 of 77 in Polk County — solidly in the upper half of the local distribution.

An invasive species record — Chinese Mystery Snail — has been logged at Big Lake; Wisconsin DNR maintains the official infested-waters list. Walleye are documented at Big Lake, one of 4 fish species on record for the lake. A documented public access point at Big Lake makes the lake usable for shore fishing, paddle craft, and trailered boats. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.