Waterways play a crucial role in Spain's geography, agriculture, and history, though the country's interior is largely arid.
**Major Rivers:** * **Tagus (Tajo):** The longest river on the Iberian Peninsula, passing through Toledo before entering Portugal. * **Ebro:** The longest river entirely within Spain, creating a fertile delta before emptying into the Mediterranean. * **Guadalquivir:** The only great navigable river in Spain, flowing through Seville. * **Douro (Duero):** Central to the country's prominent wine-growing regions.
**Coasts & Lakes:** Spain is surrounded by the Atlantic Ocean, the Bay of Biscay (Cantabrian Sea), and the Mediterranean Sea. While large natural lakes are rare, *Lake Sanabria* in Zamora is the largest glacial lake in the Iberian Peninsula. The country relies heavily on a massive network of artificial reservoirs (*embalses*) for water management.