Pine Mountain Lake

Pine Mountain Lake earns an A — water clarity, phosphorus, and chlorophyll-a all rate among the best monitored waters in Cass County. Sub-grades cluster within a single letter of each other, which usually means the lake is in stable trophic balance rather than fighting one specific stressor.

The lake's low TSI puts it in oligotrophic territory — the cleanest of the four trophic classes, but also the most vulnerable to nutrient-driven shifts. Pine Mountain Lake is unusually deep for Minnesota at 80 ft, which buffers the lake against summer warming and helps the deep water stay oxygenated. Pine Mountain Lake covers 1,617 acres alongside 9.4 miles of shoreline, large enough that conditions can vary meaningfully between bays. Among the 132 graded lakes in Cass County, Pine Mountain Lake sits at rank 44, above the county median.

Zebra mussel presence at Pine Mountain Lake means the lake's clarity numbers carry an asterisk — filtered water is not the same as nutrient-poor water. The fishery includes walleye alongside the lake's other 16 documented species — a notable draw for Minnesota anglers. Public access is available — the lake is on the Minnesota PCA public-access list. The lake has a partial ice record — 14 observed ice-outs, centered near Apr 16. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.