Portage Lake

On the LakeGrade scale Portage Lake grades a B, with clarity at 13.3 ft and phosphorus readings still being added placing it above the Minnesota median. The three sub-grades — clarity, phosphorus, and chlorophyll-a — track close together, so no single parameter is dragging the average.

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. Portage Lake reaches 45 ft at its deepest point — typical for Minnesota mid-sized lakes, with seasonal stratification but limited cold-water refuge. The lake is compact at 64 acres, with 2.0 miles of shoreline and little volume to buffer nutrient inputs. Portage Lake ranks 39 of 142 in Lake County — solidly in the upper half of the local distribution.

No invasive species are currently listed at Portage Lake — the lake remains off the Minnesota infested-waters roster. The state fisheries records do not list documented species for Portage Lake, which usually reflects a lack of formal fisheries survey work rather than an empty lake. No formal public access is documented at Portage Lake — most use is by shoreline residents and their guests. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.