Guadiana

The Guadiana River ( , , , ) is an international river defining a long stretch of the Portugal-Spain border, separating Extremadura and Andalusia (Spain) from Alentejo and Algarve (Portugal). The river's basin extends from la Mancha and the eastern portion of Extremadura to the southern provinces of the Algarve; the river and its tributaries flow from east to west, then south through Portugal to the border towns of Vila Real de Santo António (Portugal) and Ayamonte (Spain), where it flows into the Gulf of Cádiz. With a course that covers a distance of , it is the fourth-longest in the Iberian Peninsula, and its hydrological basin extends over an area around (the majority of which lies within Spain). In Portuguese, the name Guadiana has replaced Odiana, now an archaic form.

==Etymology== thumb|left|The Guadiana drainage basin in the Iberian peninsula Ptolemy's Geography recorded the Celtiberian name as Anas, meaning a marshy area or bayou. The Romans adapted this name as , which was etymolygised as the "River of Ducks". After the Muslim conquest of the Iberian Peninsula, the name was extended and referred to as Wadi Ana, later passed on to Portuguese and Spanish settlers as the Ouadiana, and later just Odiana. Since the 16th century, the name slowly evolved to take on the form Guadiana, a cognitive variation that developed from many Andalusi river placenames beginning in wadi using the prefix guad- such as the hydronyms Guadalquivir, Guadalete, and Guadarrama.