Osakis Lake

The LakeGrade rubric puts Osakis Lake at a C: clarity at 10.5 ft, 77 µg/L of phosphorus, and a TSI of 55 signal an intermediate trophic state. Of the three parameters, phosphorus is the worst — at 77 µg/L of phosphorus, it keeps the lake susceptible to algal blooms in warm years.

At a TSI of 55, Osakis Lake reads as eutrophic — nutrient-rich enough that summer algal growth and reduced clarity are expected, not unusual. The lake's 73 ft maximum depth is in the upper tier for Minnesota — deep enough for cold-water fish to find refuge in summer. With 6,389 acres of surface and 26.8 miles of shoreline, Osakis Lake is a large water by Minnesota standards — recreational pressure is spread across a long shoreline. Within the 17 graded lakes of Todd County, Osakis Lake sits at rank 13, near the bottom of the county list.

Zebra mussels have been documented at Osakis Lake, which alters the filter-feeding balance and can paradoxically increase water clarity while disrupting the food web. The fishery includes walleye alongside the lake's other 18 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 long ice-out record — 428 observations on file, with a median ice-out around Apr 19. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.