 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 of approximately (the majority of which lies within Spain).The Romans referred to the river as the , the "River of Ducks".During the Moorish occupation and settlement, the name was extended and referred to as "Wadi Ana" ("wādī" being the Arab term for "river"), later passed on to Portuguese and Spanish settlers as the Ouadiana, and later just Odiana.