Portage Lake

Portage Lake earns an A — water clarity, phosphorus, and chlorophyll-a all rate among the best monitored waters in Cass County. The three sub-grades — clarity, phosphorus, and chlorophyll-a — track close together, so no single parameter is dragging the average.

A TSI value of 32 puts Portage Lake in the oligotrophic range, where biological productivity stays low and the water column remains clear. Portage Lake is unusually deep for Minnesota at 84 ft, which buffers the lake against summer warming and helps the deep water stay oxygenated. Portage Lake covers 277 acres alongside 3.1 miles of shoreline — a mid-sized water that supports a working fishery without being so large that conditions diverge between basins. Among the 133 graded lakes in Cass County, Portage Lake ranks 10 — in the top quartile locally.

Portage Lake has no invasive species recorded in Minnesota state databases as of 2023, though prevention practices still apply at all access points. The fishery includes walleye alongside the lake's other 10 documented species — a notable draw for Minnesota anglers. The lake lacks a documented public access point, so visitor use is limited. The lake has a partial ice record — 7 observed ice-outs, centered near Apr 27. 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.