Afonso Gonçalves Baldaia in the context of "Terceira Island"

Río de Oro (Spanish: [ˈri.o ðe ˈoɾo] , Spanish for "River of Gold"; Arabic: وادي الذهب, Wādī-aḏ-Ḏāhab, often transliterated as Oued Edhahab) is the southern geographic region of Western Sahara. It was, with Saguia el-Hamra, one of the two territories that formed the Spanish province of Spanish Sahara after 1958; it had been taken as a Spanish colonial possession in the late 19th century. Its name seems to come from an east–west river which was supposed to have run through it. The river was thought to have largely dried out – a wadi, as the name indicates – or have disappeared underground.

The Spanish name is derived from its previous name Rio do Ouro, given to it by its Portuguese discoverer Afonso Gonçalves Baldaia in 1436. The Portuguese prince Henry the Navigator dispatched a mission in 1435, under Gil Eanes and Baldaia, to find the legendary River of Gold in western Africa. Going down the coast, they rounded the al-Dakhla peninsula in present-day Western Sahara and emerged into an inlet, which they excitedly believed to be the mouth of the River of Gold (see Senegal River). The name continued to be used for the inlet and the surrounding area although no gold was found there, neither in the water of the narrow gulf, probably mistaken for the river itself, nor in its neighborhood. Some gold dust, however, was obtained from the natives.