The Duero river rises in the province of Soria, in the sources of the Duero de los Picos de Urbión (2160 mbsl), in the municipality of Duruelo de la Sierra. From a geological point of view, the Duero river basin is constituted of a well-defined geological unit, the Duero Depression and its borders: the Cantabrian, Iberian and Central Mountain Ranges and the Galaico-Leoneses Mountains. The Duero River is the most important river in the northwest of the Iberian Peninsula and, with a length of 897 km, it is the third longest river in the peninsula. The international hydrographic demarcation of the Duero is the largest in the Iberian Peninsula with 98,073km2, and includes the territory of the Duero river basin, as well as the transitional waters of the Porto Estuary and the associated Atlantic coastal waters. The Duero flows into the Atlantic Ocean, specifically in Porto (Portugal).
