Deelen is one of the few remnants of an extensive peat bog landscape that once covered north-western Overijssel and Friesland. It is an area of former peat workings along the small River Boorne, comprising open water, channels (“petgaten”), reedbeds, shrubs and wet meadows. The Site boundary was adjusted to match that of the Natura 2000 Site in 2013. The Site provides breeding ground for nationally threatened birds such as bittern (Botaurus stellaris) and black tern (Chlidonias niger). It regularly supports more than 20,000 wintering waterbirds and more than 1% of the European populations of gadwall (Mareca strepera), northern shoveler (Spatula clypeata) and greater white-fronted goose (Anser albifrons). It is also very important for flood regulation and groundwater replenishment. Human activities include reed harvesting, farming, peat extraction, water management and recreation. The main threats to the Site’s ecological character derive from drainage and nutrient pollution from the surrounding farmland. The Dutch Bird Research Organisation coordinates a national bird monitoring programme at the Site.