O'Reilly Lake

O'Reilly Lake earns an A — water clarity, phosphorus, and chlorophyll-a all rate among the best monitored waters in Itasca 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. O'Reilly Lake is unusually deep for Minnesota at 79 ft, which buffers the lake against summer warming and helps the deep water stay oxygenated. The lake's 189 acres and 3.1 miles of shoreline put it in the mid-range bucket — large enough for varied use, small enough that watershed inputs reach the whole basin. O'Reilly Lake ranks 34 of 141 in Itasca County, putting it in the upper tier of locally monitored lakes.

O'Reilly Lake has no invasive species recorded in Minnesota state databases as of 2024, though prevention practices still apply at all access points. Walleye are documented at O'Reilly Lake, one of 11 fish species on record for the lake. Public access is available — the lake is on the Minnesota PCA public-access list. Monitoring depth is thin here: the LakeGrade rubric is applied to a small number of sample years, and the grade will be revised as more data accumulates.