O'Brien Lake

O'Brien Lake earns an A — water clarity, phosphorus, and chlorophyll-a all rate among the best monitored waters in Crow Wing 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 35 puts O'Brien Lake in the oligotrophic range, where biological productivity stays low and the water column remains clear. The lake's maximum depth is not yet documented in state morphometric records — context for its physical structure remains limited. The lake's surface area is not consistently recorded across state datasets — physical context remains partial. Among the 120 graded lakes in Crow Wing County, O'Brien Lake sits at rank 32, above the county median.

O'Brien Lake has no invasive species recorded in Minnesota state databases as of 2024, though prevention practices still apply at all access points. The state fisheries records do not list documented species for O'Brien Lake, which usually reflects a lack of formal fisheries survey work rather than an empty lake. A documented public access point at O'Brien Lake makes the lake usable for shore fishing, paddle craft, and trailered boats. 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.