Arcachon Bay is in the southwest sea shore of France, between the Côte d'Argent and the Côte des Landes, in the region of Aquitaine. Arcachon Bay is the last water area that remains wide opened to the ocean.

The general shape of the Bassin d'Arcachon is that of an equilateral triangle pointing north that covers an area of 150 km² at high tide and 40 km² at low tide between Cap Ferret and Arcachon city and its suburb Pyla-sur-Mer, through a 3 km narrow channel called "les Passes".

On the north shore is the town of Arès, then Andernos-les-Bains on the northeast. Just south of the entrance is The Great Dune of Pyla. Nearly in the middle of the bay is a very particular island: L'île aux Oiseaux (birds island).

It is perhaps due to the Eyre river that runs water from the Landes forest and has its mouth (Delta de l'Eyre) in its southeast corner, that the Bassin still has a link to the sea, which would otherwise be obstructed by the sandbanks brought about by the tides.