The Site is formed by artificial freshwater lakes created by the construction of dykes in the reclaimed IJsselmeer polders. In 2014 the Site was aligned with the Natura 2000 site, resulting in an increase in its area of 2,060 hectares. The lakes receive their water from the Rhine and Ijssel rivers. The Site is of international importance for endangered bird species such as bittern, spotted crake and great reed warbler. It is also particularly important for the conservation of breeding, foraging and resting bird species. The Site also supports more than 1% of the individuals of the northwestern European population of gadwall. The lakes play an important role as reservoirs for irrigating the surrounding agricultural land, while they are also used for boating, commercial fisheries, shipping traffic, water management and sand extraction. Threats include reed cutting, aquaculture and pollution with nutrients increasing eutrophication.