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A polder is an area of land reclaimed from sea or marsh; the term is generally used in connection with reclaimed land in the Netherlands, and to a lesser extent Belgium and Germany. The area is reclaimed after a dyke (embankment) has been constructed to surround it, and the water pumped out. The surface level of polderland is generally below sea-level.

Polders have been made in the Netherlands since the medieval period - Amsterdam's Schiphol Airport is constructed on a polder finally drained in the 19th century - but a major programme of reclamation was begun in the 20th century. An enclosing dike, the 20 mile long Afsluitsdijk, was built between 1927 and 1933 to close the mouth of the Zuiderzee, turning this former inlet of the North Sea into a lake. This allowed the construction of several very large polders in the newly formed IJsselmeer:

  • Wieringermeer: 1927-1930, 119 square miles
  • Noordoostpolder (North East Polder): 1937-1942, 273 square miles (including the former small islands of Schokland and Urk incorporated into the polder)
  • Oost-Flevoland (East Flevoland): completed 1957
  • Zuid-Flevoland (South Flevoland): completed 1968

Oost- and Zuid-Flevoland form one landmass, with an area of 659 square miles; it is the largest artificial island in the world. Together with the Noordoostpolder, they form the province of Flevoland, created in 1986.

A further large polder in the IJsselmeer was projected: the Markerwaard (approximately 275 square miles). The enclosing dyke was completed in 1976, but completion of the scheme was suspended on cost grounds, since supplemented by environmental concerns. The enclosed water area is known as the Markermeer.

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