Guadalquivir (gwäˌħälkēvērˈ) [key], river, c.350 mi (560 km) long, rising in the Sierra de Cazorla, SE Spain, and flowing generally SW past Córdoba and Seville into the Atlantic Ocean near Sanlúcar de Barrameda. Known to the Arabs as Wadi al-Kebir [the large river], it is the longest stream in the Andalusia region of S Spain. There are several hydroelectric plants along its course. In its middle course it flows through a populous fertile region at the foot of the Sierra Morena, where it is used extensively for irrigation. The area has a rich variety of plant life. The lower course of the Guadalquivir traverses extensive marshlands (Las Marismas) that are used for rice cultivation. The river is tidal to Seville (c.50 mi/80 km upstream), a major inland port and head of navigation for oceangoing vessels, and it is canalized between Seville and the sea.