Grindstone Lake

Grindstone Lake earns an A — every scored parameter (clarity, phosphorus, and chlorophyll-a) rates among the best monitored waters in Sawyer County. Clarity, phosphorus, and chlorophyll-a all rate similarly, so there is no obvious single lever to pull on watershed management.

The lake's low TSI puts it in oligotrophic territory — the cleanest of the four trophic classes, but also the most vulnerable to nutrient-driven shifts. At 60 ft of maximum depth, Grindstone Lake stratifies reliably through the summer — the hypolimnion stays cooler and clearer than the surface layer suggests. Grindstone Lake covers 3,176 acres alongside partial shoreline records, large enough that conditions can vary meaningfully between bays. Grindstone Lake ranks 5 of 50 in Sawyer County, putting it in the upper tier of locally monitored lakes.

Grindstone Lake has at least one documented invasive species (Banded Mystery Snail), so boaters and anglers should observe clean-drain-dry steps when leaving the lake. Walleye are documented at Grindstone Lake, one of 6 fish species on record for the lake. Multiple sampling years from the Wisconsin DNR Citizen Lake Monitoring Network back the grade, so the letter should hold steady absent a major watershed shift.