The Site includes lower stretches of the Somme River and its main tributary, the Avre, together with adjacent marshes and peatlands. At its northern (downstream) end it meets another Ramsar Site, Baie de Somme (Ramsar Site no. 925), which stretches to the river’s estuary. The Site is part of one of the largest alkaline peat complexes in north-west Europe. The excellent conservation of the Site’s peatland habitats, which is exceptional in the Atlantic biogeographical region, together with their different developmental stages, make the Site very important for animal and plant biodiversity. Notable species include the globally threatened purple small-reed Calamagrostis canescens and the European eel Anguilla anguilla. The Site is important as a wintering location for species such as the Eurasian bittern Botaurus stellaris and the Savi’s warbler Locustella luscinioides, as well as for the breeding little bittern Ixobrychus minutus, the Eurasian teal Anas crecca and the western marsh harrier Circus aeruginosus. The Site is being actively managed as a Natura 2000 site and is also protected under other designations. 70% of the population of the Somme department live close to the Site, and it is central to local farming and the leisure economy. It is of wider cultural and historic importance; the Site’s ancient fluvial terraces hold the earliest traces of human occupation in north-west Europe.