BORKUM, a low island of Germany, in the North sea, belong ing to the Prussian province of Hanover, the westernmost of the East Frisian chain, lying between the east and west arms of the estuary of the Ems. Pop. 3,911. The island, 5m. long and broad, is a favourite summer resort. There is a daily summer steamboat service with Emden (57km.), Leer and Hamburg.