This valley constitutes one of only two areas of contiguous Spain (and the only contiguous part of current Catalonia) that are located on the northern side of the Pyrenees. 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". It then reappears in the Val dera Artiga de Lin before reaching the Aran valley, then through France and eventually to the Atlantic Ocean. The Noguera Pallaresa river, whose source is only a hundred meters from that of the Garonne, flows the opposite way towards the Mediterranean.