Rock Lake

Rock Lake sits at a C on the grading scale — not impaired, not pristine, with summer measurements that vary year to year. Clarity is the limiting factor — phosphorus is reasonable but suspended particles or algal cells keep water transparency below Minnesota norms.

At a TSI of 52, Rock Lake reads as eutrophic — nutrient-rich enough that summer algal growth and reduced clarity are expected, not unusual. A maximum depth of 17 ft puts Rock Lake in the middle of Minnesota's depth distribution. The lake's 261 acres and 3.4 miles of shoreline put it in the mid-range bucket — large enough for varied use, small enough that watershed inputs reach the whole basin. Rock Lake ranks 125 of 133 in Cass County — at the lower end of the locally monitored distribution.

Rock Lake has no invasive species recorded in Minnesota state databases as of 2023, though prevention practices still apply at all access points. The fishery is bass-led, with 11 documented species across the lake's records. Public access is available — the lake is on the Minnesota PCA public-access list. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.