The national park extends from the German-Danish maritime border in the north down to the Elbe estuary in the south. In the North Frisian area, it includes the mudflats around the geest-based and marsh islands and the Halligen (undyked islands). There the mudflats are 40 km wide in places. Further south lie areas of mudflats which contain particularly large sandbanks. In addition to the plants and animals that are typical of the entire Wadden Sea, especially large numbers of porpoise, shelduck and eelgrass may be seen in the Schleswig-Holstein part