Boulder Lake

Boulder Lake earns an A — water clarity, phosphorus, and chlorophyll-a all rate among the best monitored waters in Oconto County. The three sub-grades — clarity, phosphorus, and chlorophyll-a — track close together, so no single parameter is dragging the average.

The lake sits in the mesotrophic zone — the band where most well-managed Wisconsin lakes fall. A maximum depth of just 11 ft means sediment-bound phosphorus releases back into the water column whenever wind stirs the bottom — a classic shallow-lake dynamic. The lake's 370 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. Among the 62 graded lakes in Oconto County, Boulder Lake sits at rank 22, above the county median.

Eurasian watermilfoil has been documented at Boulder Lake, requiring shoreline management to keep dense mats from crowding native vegetation. Walleye are documented at Boulder Lake, one of 5 fish species on record for the lake. 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.