Portage Lake

Portage Lake carries a solid B grade — strong on most parameters, with measurements that hold up well across the summer season. The three sub-grades — clarity, phosphorus, and chlorophyll-a — track close together, so no single parameter is dragging the average.

A TSI near 49 places Portage Lake in the mesotrophic band — moderate productivity, with seasonal swings between clearer spring water and richer late-summer conditions. The lake's 55 ft maximum depth is in the upper tier for Minnesota — deep enough for cold-water fish to find refuge in summer. At 1,539 acres, Portage Lake is one of the larger lakes in Cass County, with 7.9 miles of shoreline supporting multiple distinct use patterns. Within the 133 graded lakes of Cass County, Portage Lake sits at rank 109, near the bottom of the county list.

Zebra mussel presence at Portage Lake means the lake's clarity numbers carry an asterisk — filtered water is not the same as nutrient-poor water. Walleye are documented at Portage Lake, one of 15 fish species on record for the lake. Public access is available — the lake is on the Minnesota PCA public-access list. Multiple sampling years from Minnesota PCA volunteers and partner agencies back the grade, so the letter should hold steady absent a major watershed shift.