Arcachon Basin or alternatively Arcachon Bay (French: Bassin d'Arcachon, French pronunciation: [basɛ̃ daʁkaʃɔ̃]; Gascon: Laca d'Arcaishon) is a bay of the Atlantic Ocean on the southwest coast of France, situated in Pays de Buch between the Côte d'Argent and the Côte des Landes, in the region of Aquitaine.

[2] The general shape of the Bassin d'Arcachon is that of an equilateral triangle pointing north, the southwest corner of which is open to the sea, between Cap Ferret and the town of Arcachon (more specifically, one of the suburbs of La Teste-de-Buch, Pyla-sur-Mer), through a three-kilometre-long (2 mi) narrow channel (Les Passes).

[2] The Bassin still has a link to the sea perhaps because of the Eyre River that runs from the Landes forest and has its mouth (Delta de l'Eyre) in its southeast corner.

[2] The brackish and productive waters of the Bay of Arcachon make them ideal for hosting a wide variety of organisms, including but not limited to those belonging to the families Sparidae,[3] Mugilidae,[4] and Triglidae.

[6] Additionally, other species within the area include; Phocoenidae [37] (porpoises), Squatina [38] (angel sharks), Bathytoshia [39] (stingrays), and Crassostrea gigas [40] (oysters).