The Wadden sea is a shallow sea extending along the North Sea coasts of The Netherlands, Germany and Denmark. It is a highly dynamic ecosystem with tidal channels, sands, mud flats, salt marshes, beaches, dunes, river mouths and a transition zone to the North Sea, the offshore zone. Most parts of the Wadden Sea, in particular in The Netherlands and Lower Saxony, are sheltered by barrier islands and contain smaller or wider areas of intertidal flats. The present form of the Wadden Sea is the result of both natural forces and action by man. Twice a day, on average, 15 km3 of sea water enter the Wadden sea. With the water from the North Sea, large amount of sand and silt are imported which settle in places with little water movement. During low tides large parts of the Wadden Sea emerge. These so-called tidal flats cover about 2/3 of the tidal area and are one of its most characteristic features. Nowhere in the world can such a large unbroken stretch of tidal flats be found. They account for 60% of all tidal areas in Europe and North Africa.