a river in Switzerland, a right tributary of the Aare (Rhine Basin). It is 159 km long and drains an area of 3,425 sq km; glaciers cover 134 sq km.

The Reuss originates near the St. Gotthard Pass on the northern slopes of the Lepontine Alps. It flows across the floor of a glacial trough and then across the Lake of Lucerne (Vierwald-stätter See). The Reuss cuts through a ridge of the Swiss Pre-Alps and intersects a belt of their foothills. The mean flow rate at the mouth of the river is approximately 140 cu m per sec—the maximum flow rate occurs during summer. There are several hydroelectric power plants in the river’s basin. Luzern is located on the Reuss and the Lake of Lucerne.