Bassin de Saint-Ferréol, Artificial lake in Haute-Garonne, France.

The Bassin de Saint-Ferréol is a reservoir on the Laudot in the Montagne Noire, held back by a straight earth-and-masonry dam whose crest runs 780 m and rises 32 m, with a base over 140 m thick. Its core is granite blocks filled with rock debris and clay, and a vaulted stone tunnel pierces the base. The lake spans about 67 hectares across Vaudreuille, Sorèze and Les Brunels.

Engineer Pierre-Paul Riquet oversaw construction of this reservoir between 1667 and 1672 to supply the Canal du Midi with water throughout the year. The project was part of a larger effort to link the Atlantic Ocean with the Mediterranean Sea.

The lake takes its name from the hamlet of Saint-Ferréol on its shore, and the Languedocien form is Lac de Sant Ferriòl. Since 1930 the shore has hosted a leisure centre with tennis, sailing and swimming, a scaled-down version of a hotel-and-casino scheme proposed around 1900. The film L'Enfer (1994) was largely shot in an abandoned hotel beside the water.

Supervised swimming is available from June through September, while fishing and other water activities are possible throughout the year. Marked walking trails circle the shore, offering views of the lake and the forested slopes.

The dam's crest measures 780 metres, yet its base is more than 140 metres thick, a profile built to resist the water pressure of the reservoir. Three permanently submerged galleries carry water through the structure, and a fourth, 130 metres long, leads to the valve room where each bronze tap releases 600 litres per second.