The Site covers the more inland section of the Arcachon Basin, a large bay located near the city of Bordeaux. It features vast expanses of gallery forests, salt marshes and mudflats, and, at its south-eastern corner, the delta of the River Leyre. At the edges of the Basin are areas dammed since the 18th century for salt pans and fish farming. The wetland is important for biodiversity, including the critically endangered European eel (Anguilla anguilla), which migrates through the Site, and the brant goose (Branta bernicla), of which the Arcachon Basin harbours around 25% of the regional population. The Site delivers a variety of ecosystem services, including nutrient cycling. It also acts as a hydrological buffer zone between the wider bay and its catchment area, where freshwater from the river meets and slows down the rise of saltwater during high tides.