Douro

River in Spain and Portugal, the third-largest in the Iberian peninsula; length 775 km/482 mi. It rises in Spain, on the south side of the Peña de Urbión in the province of Soria, and flows west across the plateau of Castile. It follows the Spanish-Portuguese frontier for 105 km/65 mi, and reaches the Atlantic Ocean at São João de Foz, 5 km/3 mi south of Porto. Navigation at the river mouth is hindered by sand bars. There are hydroelectric installations along its course.

Part of the Douro valley contains the vineyards from which port wine is produced. In Spain, there are important wine-growing areas along the river in the Tierra del Vino, near Toro and Simancas.