Chain of islands, North Sea.
They extend 3 to 20 mi (5 to 32 km) off the northern European mainland, along the Dutch and German coasts and the southern part of Denmark's Jutland peninsula. Although they form a single physical feature, it is customary to subdivide them into the West Frisian Islands (held by The Netherlands), East Frisian Islands (Germany), and North Frisian Islands (Germany and Denmark). After the North Sea established a southwestern outlet to the Atlantic about 7,0005,000 BC, its southeasterly shore probably coincided with the present curve of the Frisians. Periodic subsidence, storms, and flooding have since produced this long chain of islands separated from the mainland by a narrow belt of shallow waters and tidal mud flats. The Dutch and German governments have spent large sums to protect the islands' seaward coasts and reclaim the land for farming. The beaches and resorts attract many tourists.