 Hence, this valley holds the only Catalan rivers to flow into the Atlantic Ocean (for the same reason, the region is characterized by an Atlantic climate, instead of a Mediterranean one).The Garonne river flows through Aran from its source on the Pla de Beret (Beret Flat) near the Port de la Bonaigua.It is joined by the Joèu river (from the slopes of Aneto mountain) which passes underground at the "Forau de Aigualluts".