Located in the municipality of Pobla de Benifassà. This is the confluence of four ravines: Fou (or River Sénia), Teulatí, Tenalla and Pobla (or River Verd). It provides water to the irrigation communities of Ulldecona, La Sénia, Sant Rafel and Rossell. It was built during the 1960s, financed by labourers from Ulldecona (hence the name); it is 817 ha and has a capacity of 11 Hm³. It has a gravity dam. The dam is 54 m high and 180 m wide. This dam belongs to the Júcar Hydrographical Confederation.