Enclosing Dike

The Afsluitdijk is a major dike 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 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.
Construction progressed better than expected; at three points along the line of the dike there were deeper underwater trenches where the tidal current was much stronger than elsewhere. These had been considered to be major obstacles to completing the dike, but all of them proved to be relatively straightforward. On May 28, 1932, two years earlier than initially thought, the Zuiderzee ceased to be. The IJsselmeer was born, even though it was still salty at the time.
The dike itself however was not finished yet as it still needed to be brought up to its required height and a road linking Friesland and North Holland also remained to be built. It would not be until September 25, 1933, that the Afsluitdijk was officially opened, with a monument marking the spot where the dike had been closed.
Beside the dam itself there was also the necessary construction of two complexes of shipping locks and discharge sluices at both ends of the dike. The complex at Den Oever includes the Stevin lock and three series of five sluices for discharging the IJsselmeer into the Wadden Sea; the other complex at Kornwerderzand is composed of the Lorentz locks and two series of five sluices, making a total of 25 discharge sluices. Periodically discharging the lake is necessary since it is continually fed by rivers and streams (most notably the IJssel river that gives its name to the lake) and polders draining their water into the IJsselmeer.