Wadden Sea is an interidal zone in the southeastern part of the North Sea. It lies between the coast of northwestern continental Europe and the range of Frisian Islands, forming a shallow body of water with tidal flats and wetlands. It is rich in biological diversity. In 2009, the Dutch and German parts of the Wadden Sea were inscribed on UNESCO's World Heritage List.The Wadden Sea stretches from Den Helder in the Netherlands in the southwest, past the great river estuaries of Germany to its northern boundary at Skallingen north of Esbjerg in Denmark along a total length of some 500 km and a total area of about 10,000 km².
The islands in the Wadden Sea are called the Wadden Sea Islands or Frisian Islands, named after the Frisians.