Douro (Portuguese, Douro; Spanish, Duero; ancient Durius), river of the Iberian Peninsula. It rises in Soria Province, north central Spain, and empties, after a course of 895 km (556 mi), into the Atlantic Ocean near Porto, Portugal. The general course is west to the boundary of Spain and Portugal, then south-west, delimiting the boundary for about 97 km (60 mi), and finally again west across Portugal to its mouth. Navigation on the river is possible in Portugal but is hampered by rapids and occasional floods in the lower reaches; sandbars at the mouth permit only shallow-draft vessels to enter. Of greater economic importance than navigation are the Douro irrigation projects in Spain and the expanding development of the hydroelectric potential of the river in Portugal. At Leixões, the port for Porto north of the mouth of the Douro, a harbour accommodating seagoing vessels has been constructed. The river yields fish and serves as a means of transport to market for the port and other wines of the Paíz do Vinho region of Portugal.