Borkum is an island in the Leer District in Lower Saxony, northwestern Germany. It has an area of about 30.6 km² and a population of about 5.587. Borkum is bordered to the west by the Westerems strait (which forms the border with the Netherlands), to the east by the Osterems strait, to the north by the North Sea, and to the south by the Wadden Sea. It is the westernmost of the East Frisian Islands in the North Sea, due north of the Dutch province of Groningen.Borkum formed from two islands which were still parted by a flow of shallow water in 1863. The seam between the former eastern and western parts is called Tüskendör (‘through in between’).