HERGISWILLOPPER Wastewater Treatment Plant, Hergiswil (NW), Nidwalden, Switzerland

HERGISWILLOPPER is a wastewater treatment plant located in Hergiswil (NW), in the canton of Nidwalden, Switzerland. The facility serves a population of around 7,300 residents, placing it in the small-to-medium agglomeration category under Swiss water protection regulations. Switzerland enforces strict water protection laws under the Federal Water Protection Act (GSchG), which requires all wastewater treatment plants to meet high standards. For plants of this scale, secondary treatment with nutrient removal is standard, often including biological treatment and phosphorus elimination to protect sensitive Alpine lakes and rivers. The plant's treated effluent flows into the local water system, which ultimately drains into Lake Lucerne (Vierwaldstättersee), a deep Alpine lake that supports diverse aquatic life and is a key recreational and ecological resource. The lake is part of the Reuss river basin, which flows into the Aare and then the Rhine, eventually reaching the North Sea.

The treated wastewater from HERGISWILLOPPER enters the local drainage network that feeds into Lake Lucerne, a large Alpine lake known for its clear waters and ecological sensitivity. The lake supports fish species such as lake trout and Arctic char, and its outflow forms the Reuss River, which joins the Aare and ultimately the Rhine. Protecting water quality in this watershed is critical due to the lake's role in regional biodiversity and tourism.