The Tagus is the longest river in the Iberian Peninsula, stretching for 1, 007 km (626 mi) from its source in the Montes Universales mountain range in Spain to its outlet in the Atlantic Ocean near Lisbon, Portugal. It is the second longest river in the Iberian Peninsula after the Douro. The Tagus is an important waterway for both countries, providing irrigation, hydroelectricity, and transportation.