Portage Lake

On the LakeGrade scale Portage Lake grades a B, with clarity at 12.0 ft and phosphorus readings still being added placing it above the Minnesota median. Clarity, phosphorus, and chlorophyll-a all rate similarly, so there is no obvious single lever to pull on watershed management.

Mesotrophic conditions dominate at Portage Lake: enough nutrients for a healthy fishery, not so much that algal blooms become a chronic problem. The lake's 65 ft maximum depth is in the upper tier for Minnesota — deep enough for cold-water fish to find refuge in summer. At 361 acres, Portage Lake fits the Minnesota median for monitored lakes, with 3.6 miles of shoreline. Within Cass County's 133 graded lakes, Portage Lake ranks 91 — below the local median, though not at the bottom.

Portage Lake has no invasive species recorded in Minnesota state databases as of 2021, though prevention practices still apply at all access points. Walleye are documented at Portage Lake, one of 13 fish species on record for the lake. No formal public access is documented at Portage 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.