Thunder Lake

Thunder Lake earns an A — water clarity, phosphorus, and chlorophyll-a all rate among the best monitored waters in Marinette County. Clarity, phosphorus, and chlorophyll-a all rate similarly, so there is no obvious single lever to pull on watershed management.

A TSI value of 28 puts Thunder Lake in the oligotrophic range, where biological productivity stays low and the water column remains clear. The lake's 62 ft maximum depth is in the upper tier for Wisconsin — deep enough for cold-water fish to find refuge in summer. The lake's 133 acres and partial shoreline records put it in the mid-range bucket — large enough for varied use, small enough that watershed inputs reach the whole basin. Within Marinette County's 22 graded waters, Thunder Lake sits at rank 4, near the top of the local distribution.

Thunder 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 is bass-led, with 3 documented species across the lake's records. 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.