Spanning more than 2,500 square kilometres and three French departments – Aube, Marne and Haute-Marne – this Site features a wide range of wetland habitats, including rivers, tree-dominated freshwater wetlands, reservoirs, and hundreds of ponds of which many are used for traditional fishing. It shelters characteristic species and almost 150,000 birds in winter, with some species such as the northern pintail (Anas acuta) exceeding 1% of their regional population. The Site also supports nationally endangered birds at other vulnerable life stages, notably during breeding and migration seasons, when species such as the black stork (Ciconia nigra) and the common crane (Grus grus) stop here. The reservoirs play a key hydrological role in the Seine River basin, reducing winter and spring flood peaks and maintaining sufficient river flows during low-water periods to help secure drinking water supply to Paris and its suburbs.