The Bidasoa (, ; ) is a river in the Basque Country of northern Spain and southern France that runs largely south to north. Named as such downstream of the small town of Oronoz-Mugairi (municipality of Baztan) in the province of Navarre, the river actually results from the merge of several streams near the village Erratzu, with the stream Baztan that rises at the north-eastern side of the mount Autza (1,306 m) being considered the source of the Bidasoa. It joins the Cantabrian Sea (Bay of Biscay) between the towns of Hendaye and Hondarribia.