Portage Lake

Portage Lake earns a D — measurements through 2022 show persistent nutrient pressure that limits clarity through the summer.

A TSI in the eutrophic range signals a lake doing what nutrient-loaded waters do — supporting an active algal community at the cost of clear water. Portage Lake reaches 18 ft at its deepest point — typical for Minnesota mid-sized lakes, with seasonal stratification but limited cold-water refuge. Portage Lake covers 372 acres alongside 5.1 miles of shoreline — a mid-sized water that supports a working fishery without being so large that conditions diverge between basins. Within Aitkin County's 53 graded lakes, Portage Lake ranks 38 — below the local median, though not at the bottom.

No invasive species are currently listed at Portage Lake — the lake remains off the Minnesota infested-waters roster. The fishery is bass-led, with 11 documented species across the lake's records. A documented public access point at Portage Lake makes the lake usable for shore fishing, paddle craft, and trailered boats. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.