Lake St. Croix

Lake St. Croix carries a solid B grade — strong on most parameters, with measurements that hold up well across the summer season. Clarity is the limiting factor — phosphorus is reasonable but suspended particles or algal cells keep water transparency below Minnesota norms.

Mesotrophic conditions dominate at Lake St. Croix: enough nutrients for a healthy fishery, not so much that algal blooms become a chronic problem. Lake St. Croix is unusually deep for Minnesota at 78 ft, which buffers the lake against summer warming and helps the deep water stay oxygenated. At 8,393 acres, Lake St. Croix is one of the larger lakes in Washington County, with 124.5 miles of shoreline supporting multiple distinct use patterns. Lake St. Croix ranks 9 of 31 in Washington County — solidly in the upper half of the local distribution.

Eurasian watermilfoil is established at Lake St. Croix, which can dampen recreational access and pressure the native plant community. Muskie are on the species list at Lake St. Croix, alongside the lake's 36 other documented fish. No formal public access is documented at Lake St. Croix — most use is by shoreline residents and their guests. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.