Horgen Wastewater Treatment Plant: Serving Horgen on Lake Zurich, Switzerland

The Horgen wastewater treatment plant is located in the town of Horgen, situated on the shores of Lake Zurich in the canton of Zürich, Switzerland. The facility serves a population of approximately 15,500 people, making it a medium-sized agglomeration under Swiss water protection regulations. As a Swiss plant, Horgen operates under the Swiss Water Protection Act (Gewässerschutzgesetz), which mandates advanced treatment standards to protect sensitive water bodies. For agglomerations of this scale, secondary treatment with nutrient removal is typically required to meet stringent effluent quality limits. The plant discharges treated wastewater into Lake Zurich, which is part of the Rhine basin via the Limmat River. Lake Zurich serves as a critical drinking water reservoir and recreational area, requiring high treatment standards to prevent eutrophication and protect aquatic life. The lake ultimately drains into the Rhine River and the North Sea.

Horgen's treated effluent enters Lake Zurich, a large pre-alpine lake that supplies drinking water to over one million people. The lake is sensitive to nutrient loading, which can cause algal blooms and degrade water quality. The lake drains via the Limmat River into the Aare and then the Rhine, eventually reaching the North Sea. Protecting Lake Zurich's oligotrophic status is a key environmental priority.