River, Spain and Portugal.
One of the longest in the Iberian Peninsula , it flows 483 mi (778 km) through south-central Spain and southeastern Portugal, forming parts of the countries' borders, to the Gulf of Cádiz. Its headwaters rise in the mountains of Spain's Cuenca province; west of Daimiel they form marshy lakes, known as Ojos del Guadiana ("Eyes of the Guadiana"), a noted wildfowl sanctuary. As the river continues west, it cuts a series of gorges through the Toledo Mountains, now the site of several dams that provide hydroelectric power.