The Site it is a vast shallow freshwater lake, the largest freshwater basin in the country. IJsselmeer was cut off from the Wadden Sea by the Afsluitdijk causeway in 1932, and about 45% of the territory was reclaimed as polders. In 2014 the boundaries of the Site were aligned to those of the Natura 2000 site, resulting in an increase in area of 5,184 hectares. The Site regularly supports more than 20,000 wintering waterbirds as well as endangered bird species such as ruff (Philomachus pugnax), bittern (Botaurus stellaris), avocet (Recurvirostra avosetta) and spotted crake (Porzana porzana). IJsselmeer plays a crucial role in regulating the hydrology of the northern Netherlands. The construction of an innovative “fish migration river” in the Afsluitdijk between the IJsselmeer and the Wadden Sea was started in November 2020 which would restore brackish conditions. Human activities include tourism, commercial fisheries, and shipping traffic. The Site is threatened by artificial water level management, intensive commercial fishing, industrialization, urbanization and the construction of wind farms.