The Reuss is a river in Switzerland. With a length of 158 kilometres (98 mi) and a drainage basin of 3,425 square kilometres (1,322 sq mi), it is the fourth largest river in Switzerland (after the Rhine, Aare and Rhône). The highest point of the drainage basin is the summit of Dammastock, at 3,630 metres.
Rising in the Gotthard massif, the Reuss runs from the Urserental and continues through the Schöllenen Gorge and under the legendary Devil's Bridge (Teufelsbrücke) at St. Gotthard Pass. It runs through Lake Lucerne (German Vierwaldstättersee) and the city of Lucerne, where a pioneering needle dam (just upstream from the Spreuerbrücke) maintains the water level. It receives the Kleine Emme from Entlebuch at Emmen and Lorze from Lake Zug at Hünenberg. Near Bremgarten, the river is dammed, forming Flachsee.
The Reuss, the Aare, and the Limmat come together near Brugg at the "Watercastle of Switzerland". After the confluence the river continues as the Aar, which flows into the Rhine, which runs through Germany into the North Sea.