islands, islets and Halligen, such as Trischen, Blauort or the North Frisian Barrier Island. Under the classification of the natural regions of Germany the national park area belongs to the "Schleswig-Holstein Wadden Sea, Islands and Halligen" region within the Schleswig-Holstein Marshes, and to the major unit of the German Bight. The national park can be divided into two areas. In the north, between the Danish border and the peninsula of Eiderstedt is the North Frisian part; on the south coast of Eiderstedt up to the Elbe estuary is the Dithmarschen part. The North Frisian Wadden Sea, together with the Danish Wadden Sea, belongs to the North Sea. It is screened from the open sea by the North Frisian Islands and the Halligen. The islands were mainly formed from elements of the mainland, which became separated, mainly as a result of flood disasters. The mudflats are protected and the transition between the flats and the sea is often clearer, because the former lie to the east of the large islands and the latter to the west of them. There are no major river estuaries and the tidal range is relatively low at less than two metres. In the northern Wadden Sea there are still geest cliffs formed in the ice ages, so that the highest elevations occur here on the coast in an otherwise very flat area. The Dithmarschen part and the south coast between the Elbe and Eider estuaries form the central part of the Wadden Sea. A tidal range of over three metres has largely prevented the formation of islands. Some sandbars emerge from the sea, but only Trischen is high enough and safe enough from storm surges, to allow saltwater-loving vegetation to grow. Compared to the geologically similar East Frisian Islands of the southern Wadden Sea, Trischen is considerably smaller and younger. All attempts by human inhabitants to fortify the island have failed. With several large estuaries the salinity in the central Wadden Sea is lower than in the rest of the Wadden Sea and is subject to higher fluctuations. Protection areas of the National Park The national park divides into two zones that correspond to different levels of protection. Zone 1 has a size of 162.000 ha and covers a third of the whole national park. The zone consists of 12 bigger units which all contain marshland, intertidal estuarine mudflat, mixed sediment mudflat, sand flat, tidal creeks