Terrain and climate make Spain's rivers are generally, low and irregular flow regime. In the Galician Cantabrian slope emphasize the Bidasoa, Urumea, Nervion, Assos, Pas, Asturias Deva, Sella, Nalón, Navia, Mandeo, Tambre, Ulla and, above all, the Minho, with its tributary Sil.