The Afsluitdijk (Dutch: [ˈɑfslœydɛik] ⓘ; West Frisian: Ofslútdyk [ˈɔfslyːdik]; "closure dyke"[a]) is a major dam and causeway in the Netherlands.

However, the opening of the North Sea Canal (Noordzeekanaal) in 1876 gave a much shorter direct entrance to the Amsterdam harbour, and overfishing had depleted the shallow bay.

But after the flood of 1916 and the famine of 1918, opinions were ready for this mega project and the parliament agreed, but it took another 9 years, until 1927, before the works actually began.Wieringen was connected to the mainland with the short Amsteldiepdijk in 1925; the Afsluitdijk would be 32 kilometres (20 miles) in length.

Work started at four points: on both sides of the mainland and on two specially made construction-islands (Kornwerderzand and Breezanddijk) along the line of the future dyke.

As the dyke grew, physicist Hendrik Antoon Lorentz calculated the force of the tide as the smaller gap made it stronger.

Ten thousand workers, 27 large dredges, 13 floating cranes, 132 barges, and 88 tugs worked on the project at the end, timed to close the dyke at low tide; it was finished on 28 May 1932.

[6] Construction progressed better than expected; at three points along the line of the dyke there were deeper underwater trenches where the tidal current was much stronger than elsewhere.

Two years earlier than initially thought, the Zuiderzee ceased to be, as the last tidal trench, the Vlieter, was closed by a final bucket of till.

The dyke itself however was not finished as it still needed to be brought up to its required height and a road linking Friesland and North Holland (the current A7/E22 motorway) also remained to be built.

On 25 September 1933, the Afsluitdijk was officially opened, with a monument designed by architect Willem Marinus Dudok marking the spot where the dyke had been closed.

The majority of the dam's core consisted of sand, while boulder clay on the exterior provided resistance against water flow, limiting seepage and enhancing dike breach protection.

[1][8] During construction, the slopes were partially fortified with basalt columns and Belgian block stone Belgische Bloksteen, a block-shaped, hard variety of limestone.

Although the 1953 water level was not as extreme at the Afsluitdijk as in the southern Netherlands, the intense wave action resulted in severe damage to a large portion of the block stone, which was later replaced by basalt.

[1][8] On 23 September 1954, on the centenary of Cornelis Lely, a statue, made by Mari Andriessen, was unveiled by Queen Juliana on the North Holland side of the Afsluitdijk.

In 2012, the State Secretary for Infrastructure and the Environment, Joop Atsma, issued a statement detailing the factors influencing the decision to replace the locks at Kornwerderzand.

[needs update] Provision for a railway line linking North Holland and Friesland (between Anna Paulowna and Harlingen) had been included on the Afsluitdijk, in the form of a linear reservation, along with extra drawbridge abutments at the locks.

The reservation and abutments for the rail line were utilized instead for a second carriageway for the dyke's two-lane highway in the 1970s, transforming the latter into today's four-lane A7 motorway.