O'Brien Lake

On the LakeGrade scale O'Brien Lake grades a B, with clarity at 19.7 ft and 21 µg/L of phosphorus placing it above the Minnesota median. Sub-grades cluster within a single letter of each other, which usually means the lake is in stable trophic balance rather than fighting one specific stressor.

The lake sits in the mesotrophic zone — the band where most well-managed Minnesota lakes fall. 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. Within Dakota County's 36 graded waters, O'Brien Lake sits at rank 2, near the top of the local distribution.

O'Brien Lake carries an invasive watermilfoil record — boat-launch decontamination and shoreline care matter more here than at uninfested lakes. 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. The lake lacks a documented public access point, so visitor use is limited. The grade is supported by multiple sampling years from Minnesota PCA volunteers and partner agencies, giving the letter a reasonably stable foundation.