Bonnie Lake

The LakeGrade rubric puts Bonnie Lake at a C: clarity at 8.5 ft, phosphorus readings still being added, and a TSI of 46 signal an intermediate trophic state. 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.

A TSI near 46 places Bonnie Lake in the mesotrophic band — moderate productivity, with seasonal swings between clearer spring water and richer late-summer conditions. A maximum depth of just 11 ft means sediment-bound phosphorus releases back into the water column whenever wind stirs the bottom — a classic shallow-lake dynamic. The lake's 105 acres and 2.5 miles of shoreline put it in the mid-range bucket — large enough for varied use, small enough that watershed inputs reach the whole basin. Within Lake County's 142 graded lakes, Bonnie Lake ranks 98 — below the local median, though not at the bottom.

Bonnie 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 Bonnie Lake, which usually reflects a lack of formal fisheries survey work rather than an empty lake. No formal public access is documented at Bonnie Lake — most use is by shoreline residents and their guests. 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.