High Quality Content by WIKIPEDIA articles! The Douro or Duero (Portuguese: Douro, IPA: or ; Spanish: Duero, IPA: ; Latin: Durius) is one of the major rivers of the Iberian Peninsula, flowing from its source near Duruelo de la Sierra in Soria Province across northern-central Spain and Portugal to its outlet at Porto. Its total length is 897 km, of which only sections of the Portuguese reaches of the river are navigable, by light rivercraft.