The East Frisian Islands – Ostfriesische Inseln, are a chain of islands in the North Sea, off the coast of East Frisia in Lower Saxony, Germany. The islands extend for some 90 kilometres (56 mi) from west to east between the mouths of the Ems and Jade / Weser rivers and lie about 3.5 to 10 km offshore. Between the islands and the mainland are extensive mudflats, known locally as Watten, which form part of the Wadden Sea. In front of the islands are Germany’s territorial waters, which occupy a much larger area than the islands themselves. The islands, the surrounding mudflats and the territorial waters (The Küstenmeer vor den ostfriesischen Inseln nature reserve) form a close ecological relationship. The island group makes up about 5% of the Lower Saxony Wadden Sea National Park.
The largest island by surface area is Borkum, located at the western end of the chain; the other six inhabited islands are from west to east: Juist, Norderney with the largest town in the islands, Baltrum Langeoog, Spiekeroog andWangerooge. There are also four other small, uninhabited islands: Lütje Hörn east of Borkum, Memmert and Kachelotplate southwest of Juist, Minsener Oog, a dredged island southeast of Wangerooge, and Mellum at the eastern end of the island chain which, following the boundary revision by the Federal Office for Nature Conservation, no longer belongs to the East Frisian Islands, but to the mudflats of the Elbe-Weser Triangle (Watten im Elbe-Weser-Dreieck).
Even though today they are established islands, some of them continue to be in motion. On the East Frisian island of Juist for example, since the year 1650 there are five different proven sites for the church, as the spot for rebuilding the church had to keep pace with the ever-moving island. At times, Juist even consisted of two islands, which eventually grew back together. The neighboring island of Wangerooge in the last 300 years has moved a distance equivalent to its own length to the east, its church tower, destroyed at the outbreak of World War I apparently moving from east to west. In this process, land is slowly eroded on the western coasts, while sediments are deposited on the eastern coasts. As a result, western coasts are increasingly protected by human action. The canals between the islands serve as passages for the tides, so that in these places the scouring action of current prevents the islands gradually joining one to another.