Åsnen is a large, shallow nutrient-poor freshwater lake with bays and islands. On the north side are meadows and marshland which flood regularly. Vegetation includes coniferous and deciduous forest, scattered scots pine, and several bogs. The interaction between the freshwater and terrestrial habitats enables the extraordinarily rich biodiversity within the Site and its surroundings. The lake supports a rich variety of fish, including rare species such as the critically endangered European eel Anguilla anguilla, which encourage a vast community of breeding birds including the nationally threatened black tern Chlidonias niger. It is also an internationally important staging area for migratory Anatidae (ducks, geese, swans), including large numbers of bean goose Anser fabalis, greyleg goose Anser anser, and common merganser Mergus merganser; in total 35,000 waterbirds are regularly supported by the Site. Management plans for the overlapping Natura 2000 sites and the Nature Reserves are being implemented.