The Guadiana (, ), or Odiana, is an international river located on the Portuguese–Spanish border, separating Extremadura and Andalucia (Spain) from Alentejo and Algarve (Portugal). The river's basin extends from the eastern portion of Extremadura to the southern provinces of the Algarve; the river and its tributaries flow from east to west, then south 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 829 km, it is the fourth-longest in the Iberian peninsula, and its hydrological basin extends into an area of approximately 68,000 km² (the majority of which lies within Spain).

Read more about Guadiana:  Etymology, River Basin, Estuary