Portage Lake

Portage Lake earns a D — measurements through 2022 show persistent nutrient pressure that limits clarity through the summer. Clarity, phosphorus, and chlorophyll-a all rate similarly, so there is no obvious single lever to pull on watershed management.

At a TSI of 55, Portage Lake reads as eutrophic — nutrient-rich enough that summer algal growth and reduced clarity are expected, not unusual. Portage Lake reaches 18 ft at its deepest point — typical for Minnesota mid-sized lakes, with seasonal stratification but limited cold-water refuge. At 372 acres, Portage Lake fits the Minnesota median for monitored lakes, with 5.1 miles of shoreline. Portage Lake sits at rank 38 of 53 in Aitkin County, in the lower half of the local distribution.

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. Public access is available — the lake is on the Minnesota PCA public-access list. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.