Loon Lake Deep

The LakeGrade rubric puts Loon Lake Deep at a C: clarity at -324.8 ft, 23 µg/L of phosphorus, and a TSI of 50 signal an intermediate trophic state. Secchi readings are the weakest of the three parameters, suggesting suspended sediment or algal biomass dominates the optical signal.

A TSI near 50 places Loon Lake Deep in the mesotrophic band — moderate productivity, with seasonal swings between clearer spring water and richer late-summer conditions. 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 Cook County's 128 graded lakes, Loon Lake Deep ranks 84 — below the local median, though not at the bottom.

Loon Lake Deep has no invasive species recorded in Minnesota state databases as of 2022, though prevention practices still apply at all access points. The state fisheries records do not list documented species for Loon Lake Deep, which usually reflects a lack of formal fisheries survey work rather than an empty lake. The grade is supported by multiple sampling years from Minnesota PCA volunteers and partner agencies, giving the letter a reasonably stable foundation.