Mequinenza or Mequinensa is a town and municipality of the province of Zaragoza, in the autonomous community of Aragon, Spain. It is located beside the river Segre, close to its confluence with the river Ebro between the Mequinenza Dam and Riba-roja reservoir. Its reservoir, known also as Mar de Aragón, built between 1957 and 1964, has a capacity of 1,530,000,000 m3 and is one of the largest in the country.