This important wetland is a typical river delta that encompasses several valuable habitats such as brackish coastal lagoons and salt marshes, wetlands, coastal sandy areas and, to a lesser extent, some river islands and freshwater springs (known as "ullals"). It is the largest and most important wetland in Catalonia and one of the most remarkable, in extension and biodiversity, in the western Mediterranean; it also has great importance for the maintenance of fisheries in the region. From a biodiversity point of view the Ebro Delta has international importance, holding some halophytes and aquatic plant communities (including a large number of rare and endangered species), and several species of endemic threatened fish, although the site is particularly noted for waterbirds: the population of nesting waterfowl rises to 56,000 pairs, reaching the wintering numbers up to 200,000 individuals, and it is relevant the presence of the world’ largest colony of the endemic Audouin's Gull (60-70% of the world population).