In the first instance, the Oosterschelde would be closed off by a normal dam. In 1967, the reclamation of three working islands had already started, after which it would only be a matter of pouring concrete to close off the Oosterschelde . However, people began to realize that the closure of the Oosterschelde had all kinds of consequences. Safety was important, but nature should not be forgotten either. One solution was to keep the Oosterschelde open and the 150 km dike around the Oosterscheldesystematically increase. In 1975, however, the then cabinet came with the proposal to build an open barrier that could be closed. The barrier would consist of pillars between which slides were hung that could close off the Oosterschelde in an emergency . In 1979 the parliament approved this plan. Two auxiliary dams should also be built, the Philipsdam and the oesterdam . This limited the surface of the Oosterschelde and strengthened the tidal effect. A tidal-free shipping route would be created between Antwerp and the Rhine.

The landscape around the Oosterschelde is unique in the world. The variety of life is great: there are more than 70 fish species, 140 types of aquatic plants and algae, 350 types of benthic animals and between 500 and 600 animal species on land. The Oosterschelde is also an important area for birds looking for food, breeding or looking for a place to hibernate . If the Oosterschelde was closed, this unique saltwater environment would disappear together with mussel and oyster cultivation, which would also have economic consequences. Fishing was the main source of income for traditional fishing towns such as Yerseke and Bruinisse. Oyster farming has been involved in the Oosterschelde since 1870 .