Arcachon Bay (in French, the Bassin d'Arcachon, and known locally simply as le Bassin) is a bay of the Atlantic Ocean on the southwest coast of France, situated in Pays de Buch between the C?te d'Argent and the C?te des Landes, in the region of Aquitaine. The bay covers an area of 150 km? at high tide and 40 km? at low tide. Some of its geological features are natural preservation areas