Mary Lake

On the LakeGrade scale Mary Lake grades a B, with clarity at 9.8 ft and 19 µg/L of phosphorus placing it above the Minnesota median. Clarity is the limiting factor — phosphorus is reasonable but suspended particles or algal cells keep water transparency below Minnesota norms.

Mesotrophic conditions dominate at Mary Lake: enough nutrients for a healthy fishery, not so much that algal blooms become a chronic problem. Mary Lake reaches 40 ft at its deepest point — typical for Minnesota mid-sized lakes, with seasonal stratification but limited cold-water refuge. At 2,450 acres, Mary Lake is one of the larger lakes in Douglas County, with 11.7 miles of shoreline supporting multiple distinct use patterns. Within Douglas County's 51 graded lakes, Mary Lake ranks 28 — below the local median, though not at the bottom.

Mary Lake is on the Minnesota infested-waters list for zebra mussels — boaters should follow clean-drain-dry protocols when moving gear to or from the lake. The fishery includes walleye alongside the lake's other 17 documented species — a notable draw for Minnesota anglers. A documented public access point at Mary Lake makes the lake usable for shore fishing, paddle craft, and trailered boats. The lake has a long ice-out record — 49 observations on file, with a median ice-out around Apr 16. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.