The "little sister" of the Baie de Somme, the Baie d'Authie forms the natural frontier between the Somme and Pas-de-Calais. This area is protected as part of a regional marine nature park (Parc Naturel Marin des Estuaires Picards et de la Mer d'Opale) and also offers the unique sight of a colony of grey seals and harbour seals resting on the sand banks at low tide.