Guadiana (Wadi Ana, Anas, Guadiana, Guadiana, pron. gwɐdi'ɐnɐ, or Odiana) is one of the major rivers of Spain and Portugal. It forms part of the border between the two countries, separating Extremadura and Andalucia (Spain) from Alentejo and Algarve (Portugal).
It is 742 kilometers long and drains an area of about 67,000 square kilometers. It flows into the Gulf of Cadiz, part of the Atlantic Ocean, between Vila Real de Santo António (Portugal) and Ayamonte (Spain). In Spain the river flows east to west,then flows south,in Spain and Portugal.
Badajoz, Spain, is the largest city on the river. The largest Portuguese cities along the Guadiana are: Elvas, Moura, Serpa and Vila Real de Santo António, the latter is 2 km from its mouth. There are nearly two thousand dams on the river, the largest of which is the Alqueva dam, near Moura, in Beja district, in Portuguese territory.