The Sihl is a Swiss river that rises near the Druesberg mountain in the canton of Schwyz, and eventually flows into the Limmat in the centre of the city of Zürich, after crossing the Zürich–Winterthur railway at Zürich HB. It has a length of 73 km, including the Sihlsee reservoir, through which the river flows. Water is abstracted from the river at the Sihlsee, leading to decreased downstream water flows and a consequent reduction in water quality.
