Nesslau Churfirsten Wastewater Treatment Plant, Stein (SG), St. Gallen, Switzerland

Nesslau Churfirsten is a wastewater treatment plant located in Stein (SG), within the municipality of Nesslau in the Wahlkreis Toggenburg district of St. Gallen, Switzerland. The plant serves a population of approximately 9,577 people, placing it in the small to medium agglomeration category under Swiss and EU regulatory frameworks. As a Swiss plant, Nesslau Churfirsten operates under the Swiss Water Protection Act (Gewässerschutzgesetz), which mandates appropriate treatment levels based on the sensitivity of receiving waters. For agglomerations of this size, secondary treatment is typically required, with potential for additional nutrient removal if discharging into sensitive areas. The treated effluent from Nesslau Churfirsten ultimately discharges into local watercourses that drain into the Thur River, a tributary of the Rhine. The Rhine flows through Switzerland, Germany, and the Netherlands before reaching the North Sea. The local watershed supports diverse aquatic life and is part of the larger Rhine basin, which is ecologically significant for migratory fish species and overall biodiversity.

The plant discharges into the local watershed that feeds the Thur River, a major tributary of the Rhine. The Rhine basin is a critical ecological corridor supporting diverse aquatic species, including migratory fish like salmon and eel. Downstream, the Rhine flows through several countries before reaching the North Sea, making water quality management in this region important for transboundary environmental health.