Shell Lake STP - Secondary Wastewater Treatment Plant in Shell Lake, Wisconsin

Shell Lake STP is a municipal wastewater treatment facility located in Shell Lake, Washburn County, Wisconsin, United States. The plant serves a population of approximately 1,340 residents, reflecting a small community-scale operation typical of rural Wisconsin towns. The plant provides secondary treatment, which is the standard level required under the U.S. Clean Water Act for municipal facilities discharging to surface waters. With a designed capacity of 738.15 units and an average daily discharge of 340.69 units, the plant operates well within its capacity. As a U.S. facility, it operates under a National Pollutant Discharge Elimination System (NPDES) permit issued by the Wisconsin Department of Natural Resources, ensuring compliance with effluent limits. The treated effluent from Shell Lake STP is discharged into a local water body, likely a tributary of the St. Croix River basin, which flows southward to the Mississippi River and ultimately to the Gulf of Mexico. The plant's location inland and away from coastal areas reduces direct marine impact, but its discharge contributes to the overall water quality of the Upper Mississippi River system.

The plant discharges into a local water body within the St. Croix River watershed, a tributary of the Mississippi River. The St. Croix River is a National Scenic Riverway known for its ecological significance, supporting diverse aquatic life including mussels, fish, and migratory birds. Downstream, the Mississippi River carries treated effluent to the Gulf of Mexico, where nutrient loading can contribute to hypoxic zones. The plant's secondary treatment helps reduce organic pollutants and suspended solids, protecting local stream health.