The Afsluitdijk (English: Enclosure Dam) is a major causeway in the Netherlands, constructed between 1927 and 1933 and running from Den Oever on Wieringen in North Holland province, to the village of Zurich in Friesland province, over a length of 32 km (20 miles) and a width of 90 m, at an initial height of 7.25 m above sea-level.

It is a fundamental part of the larger Zuiderzee Works, damming off the Zuiderzee, a salt water inlet of the North Sea and turning it into the fresh water lake of the IJsselmeer.