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 in the bay every day. As the tide rises, the water then encircles the sandbanks and submerges them. The people who had sought refuge there would then be trapped. 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. It is recommended to follow a guide in order to avoid getting stranded but the adventure is exhilarating.