St. Croix Lake

St. Croix Lake earns a C — middle-of-the-pack water quality, with one or two parameters dragging the average down from a stronger grade.

A TSI near 46 places St. Croix Lake in the mesotrophic band — moderate productivity, with seasonal swings between clearer spring water and richer late-summer conditions. The lake's 78 ft maximum depth is in the upper tier for Minnesota — deep enough for cold-water fish to find refuge in summer. At 8,393 acres, St. Croix Lake is one of the larger lakes in Washington County, with 124.5 miles of shoreline supporting multiple distinct use patterns. Within Washington County's 31 graded lakes, St. Croix Lake ranks 18 — below the local median, though not at the bottom.

Eurasian watermilfoil has been documented at St. Croix Lake, requiring shoreline management to keep dense mats from crowding native vegetation. St. Croix Lake's fishery is anchored by muskellunge, with 36 documented species in total — a destination water for muskie anglers. No formal public access is documented at St. Croix Lake — most use is by shoreline residents and their guests. 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.