Wieringen is a municipality in the province of North Holland. It was once an island but since 1924 Wieringen stopped being an island, because on 31 July 1924 the Amsteldiep was closed by a short dam called the Amsteldiepdijk. In 1930 the Eastern Wieringermeerdijk was completed in the Zuiderzee, and with it the adjacent polder the Wieringermeer. The closing of the Zuiderzee was completed in 1932 by the Afsluitdijk, a large dike which links Wieringen with Friesland. This dike starts at Den Oever.