Colby Lake

Colby Lake earns a C — middle-of-the-pack water quality, with one or two parameters dragging the average down from a stronger grade. Clarity is the limiting factor — phosphorus is reasonable but suspended particles or algal cells keep water transparency below Minnesota norms.

Eutrophic conditions are the baseline here: clarity drops noticeably in late summer, and dissolved oxygen near the bottom can become a concern. A maximum depth of 30 ft puts Colby Lake in the middle of Minnesota's depth distribution. Colby Lake covers 518 acres alongside 12.0 miles of shoreline — a mid-sized water that supports a working fishery without being so large that conditions diverge between basins. Within St. Louis County's 187 graded lakes, Colby Lake ranks 95 — below the local median, though not at the bottom.

Colby Lake has no invasive species recorded in Minnesota state databases as of 2024, though prevention practices still apply at all access points. The fishery includes walleye alongside the lake's other 15 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 — 10 observed ice-outs, centered near Apr 21. 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.