Seen from the coast, the bay appears to be a vast flat expanse, however this is no more than a trick of the eye. Three coastal rivers – the Sée, the Sélune, and the Couesnon – carve out new channels every day which are then flowed through by the rising tide. The water encircles the sandbanks and submerges them. As the lack of noticeable landscape reduces people's perception of distances, people always think they have time to get back before the tides come in.