Celebrated as a structure of the century, it was opened on 20 March 1973. Following the North Sea flood of 1962 which swept through Tönning, consideration was given to raising the dykes along the banks of the Eider or building a storm surge barrier at its mouth. The latter was chosen and construction work began in 1967. The current conditions in the estuary caused great difficulties and the cost of construction was correspondingly high (ca. 170 million DM = ca. 87 million euros). The line of dykes in the Eider region was shortened from 60 km to 4.8 km. The new current conditions however dug a new hole about 30 metres deep directly in front of the dyke and lock which had to be filled in during the 1980s with 20,000 sandbags.