Lat. Rhodanus, river, 505 mi (813 km) long, rising in the Rhône glacier, NE Valais, Switzerland. It flows west through a narrow, flat valley that separates the Bernese Alps from the Pennine Alps and enters Lake Geneva near Montreux. Leaving the lake at Geneva, it enters E France and is joined by the Saône River at Lyons.

Now navigable, it flows S past Valence and Avignon and separates the Massif Central from the French Alps. At Arles, at the head of the Rhône delta, the river separates into the Grand Rhône and the Petit Rhône, which join the Mediterranean Sea W of Marseilles and enclose the island of Camargue.

Both branches are silted, and a canal has been built connecting the Rhône with the port of Marseilles. With its impetuous Alpine tributaries (Isère, Drôme, Durance, and others), the Rhône has the largest water flow of all French rivers.

There are large hydroelectric power plants near Sion and Geneva (Switzerland); in France, the Génissiat Dam and allied projects are of great economic importance. Almost the entire Rhône valley S of Lyons is covered with excellent vineyards and fruit and vegetable gardens; in the extreme south silkworms are cultivated for the Lyons textile factories, and olives and flowers are important products.

The Compagnie National du Rhône sought to develop the Rhône for power production, irrigation and improved navigation; since the late 1970s the area south of Lyons has become navigable for barges of 3,000 to 5,000 tons. The Rhône-Saône valley is a principal north-south communications route in France.

An extensive canal system links the Rhône with other river systems. A series of canals linking the Saône (the principal tributary of the Rhône north of Lyons) to the Rhine allows large barges to traverse Europe from the North Sea all the way to the Mediterranean. The Rhône valley is the cradle of Provençal culture.