Guadiana (Arabic, Wadi Ana, Latin Anas, Spanish Guadiana, Portuguese Guadiana) is one of the major rivers of Spain and Portugal. It forms part of the border between the two countries.

It is 778 kilometers long and drains an area of about 67,000 square kilometers. It flows into the Gulf of Cadiz , part of the Atlantic Ocean.

Badajoz, Spain, is the largest city on the river. There are nearly two thousand dams on the river, the largest of which is called Alqueva.

United Nations Environment Program description