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. Secchi readings are the weakest of the three parameters, suggesting suspended sediment or algal biomass dominates the optical signal.

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 Wisconsin at 60 ft, which buffers the lake against summer warming and helps the deep water stay oxygenated. With 7,696 acres of surface and partial shoreline records, Lake St. Croix is a large water by Wisconsin standards — recreational pressure is spread across a long shoreline. Lake St. Croix ranks 3 of 7 in St. Croix County — solidly in the upper half of the local distribution.

Lake St. Croix is on the Wisconsin infested-waters list for zebra mussels — boaters should follow clean-drain-dry protocols when moving gear to or from the lake. Walleye are documented at Lake St. Croix, one of 7 fish species on record for the lake. Public access is available — the lake is on the Wisconsin DNR public-access list. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.