Étang de Cazaux et de Sanguinet, Artificial pond in Gironde, France.

The Étang de Cazaux et de Sanguinet is a 55 km² lake at 12 m elevation, bordered by Cazaux (La Teste-de-Buch) to the north, Sanguinet to the east and Biscarrosse to the south, between the pays de Buch and the pays de Born. Its pale green shallows reveal sandy bottoms, while the open water turns deep grey-blue; a narrow channel cuts in from the shore, and a rectangular basin near a curving sandy bank holds rows of small white boats.

The lake formed when coastal dunes blocked the Gourgue, a river from the Landes plain, raising water levels over centuries. This submerged three villages along its bed: the Gallo-Roman mansio of Losa (1st–3rd century AD), the fortified village of l'Estey du Large (3rd–1st century BC) and Put Blanc. Since the 1970s, CRESS divers have mapped Iron Age sites and recovered pine and oak dugout canoes from the old riverbed.

The museum in Sanguinet displays objects found during underwater explorations of the drowned settlements below the lake. These artifacts show how people lived in the villages before the water rose.

The lake has multiple access points along its shore where visitors can swim, sail, kayak, paddleboard, and fish. These activities are generally available year-round, with water temperature determining the most comfortable times.

Three complete ancient villages rest beneath the water's surface, representing different periods of human settlement. Diving expeditions have explored these submerged communities and recovered many artifacts now displayed in local museums.