The same method was used to close the Haringvliet as was used with the Grevelingen. Cradles that ran on and off of a cable way, plunged large concrete blocks into the water. Caissons were not used. The southern gap was the easiest to close: a cable way was not even needed. Sand was raised on the section of the dam, until a dike was formed. The southern part of the Haringvliet dam began to look more and more like a dune, particularly because of the influence of the wind and water. As a result, it is hard to determine where the dam actually starts. The remaining northern gap was one kilometre wide and much harder to close. Cableways plunged more than 100,000 concrete blocks, each weighing 2,500 kilograms, into the opening. The holes between these concrete blocks were filled with sand and as a result no water could flow between them.
During the construction of the northern and southern parts of the dam, the locks were open, because the tidal movements had to be maintained. Should the locks have been closed, the flow could have become so strong that parts of the dam would have been swept away. After the northern gap was closed, the slides could also be closed. From this moment on, the Haringvliet had become a lake.