To discover France's Baie de Somme, on the northern Picardy coast, it's best to venture out at low tide. The River Somme's vast estuary reveals an archipelago of sandbanks and salt marshes: a paradise for migratory birds, but also for sheep farmers. During a canoe trip, tourists can get close to the stars of the bay: the seals. The largest seal colony in France has taken up residence here, much to the delight of visitors.