The river has its source at in Col d'Aneu, Pyrenees, not far from the Col du Pourtalet. It then flows in the Tena Valley through the municipalities of Sallent de Gállego, Panticosa and Biescas. Starting from Sabiñánigo it forms a wide elbow until Triste, from which it continues in its primitive north-south direction until flowing into the Ebro near Zaragoza.