The Mandeo River is a river noted for its rich fish stocks, with important fishing preserves for salmon and trout, and for the celebration along its banks of the Os Caneiros pilgrimage, the largest secular pilgrimage in Galicia. The presence of numerous hydroelectric power plants along its course has, in recent years, generated significant controversy due to the alleged danger posed by sudden changes in water flow resulting from their operation. The river rises at Marco das Pías, in the municipality of Sobrado, in the province of A Coruña, at an altitude of around 700 metres. It flows through the municipalities of Sobrado dos Monxes, Aranga, Curtis, Irixoa, Coirós, Paderne and Betanzos, covering a total length of approximately 64 km. It is the second most important river of the Rías Altas, after the Eume. It flows into the city of Betanzos, where it joins the Mendo River to form the Ría of Betanzos.