The Bassin d'Arcachon is a tidal lagoon with one narrow mouth to the Atlantic, which means two quite different kinds of water within a few kilometres of each other: flat, sheltered, oyster-farmed bay on the inside, and serious ocean surf on the sandbanks outside. Almost everything bookable here follows that split.
On the bay, the traditional boat is the pinasse — long, flat-bottomed, built for shallow water — and most operators run trips out to the Île aux Oiseaux and its stilt cabins, or across to the Banc d'Arguin below the Dune du Pilat. On the ocean side, the surf schools teach at La Salie and Le Moulleau. The bird reserve at Le Teich, at the far end of the bay where the Leyre delta comes in, is the other reason people book a guide.
Tides run hard here and the sandbanks move, which is why so much of what follows involves somebody else driving.