The New Student's Reference Work/Douro

Douro (do͞o′rō), a large river of Spain and Portugal. It rises on the frontier of the province of Soria, and flows in a westerly direction until it empties into the Atlantic near Oporto. It is 500 miles long; but navigation is difficult because of rocks and sandbanks, and it is little used for commerce. It has many tributaries, the most important being the Pisuerga.