 Situated in the north-east of Spain, the river stretches some and has a basin of , of which is in Navarre and the remaining is in the province of Alava.The source of the river is to the north of the village Esteríbar, near the border with France, and it empties into the Aragón River near Funes.The river is dammed in the Eugui reservoir near Esteríbar; the dam principally serves the needs of Pamplona's metropolitan area, the largest city on the Arga.