Lagoa Comprida, was an old glacier lake with 1km of extension. Taking advantage of the covão, the construction of the dam began in 1912. In 1914, it had a height of 6 meters and in 1934 it reached 15 meters. It currently has a height of 28 meters, with elevation works done in 1965.

It is a gravity type dam, formed by 3 granite masonry arches, with 1200m of development. The volume of masonry is over 100,000 m3. The reservoir has a capacity of about 14,000,000m3 of water, flooding an area of 811,614 m2. The slope basin is 13.5km2. In this reservoir two tunnels flow; the one of Covão do Meio, of 2354m, that diverts the waters of the slopes of the Tower, and the one of Conchos, with 1519m that diverts the waters of the Ribeira das Naves.

Length of 2100m and width between 840-250m