A right-bank tributary of the Sado River. It rises in the Mendro Mountains and stretches for 70 kilometers. It has two large reservoirs, with a total area of 2,450 hectares (the Odivelas Dam and the Albergaria dos Fusos Dam). To the southwest of the reservoirs are the Patos and Paneiro lagoons, which together are part of the irrigation plan for the surrounding area.