Little past Rudagüera, in Torrelavega, the Besaya River flows into the valley until it reaches its mouth in the Ria of San Martín near Suances, flowing into the Bay of Biscay
In the vicinity of Rudagüera, in Torrelavega, the Besaya River enters a valley and eventually empties into the Ria of San Martín, which flows into the Bay of Biscay