The tides in the Eastern Scheldt would change, despite the Eastern Scheldt barrier remaining open . The estuary of the Oosterschelde was reduced in size, so that less seawater could flow in and out of the Oosterschelde . The difference between high water and low water became smaller, which endangered mudflats and salt marshes. Two dams on the east side of the Oosterschelde reduced the surface of the Oosterschelde , which strengthened the tidal effect. In the northeast, the Krammer (approximately 3,500 hectares of water) was closed off from the Oosterschelde by the Philips dam . The Oesterdam closed in the easta piece of another 1,000 hectares of water. By closing off these areas, the aim was to raise the water level in the Oosterschelde by 2.7 meters.
Oyster cultivation in Yerseke, for example, was saved by these dams, they ensured that the Scheldt-Rhine Canal was no longer hindered by the tides and, in combination with the Eastern Scheldt barrier, protected the area behind it against high water levels.
The Oesterdam is the longest Deltawerk with a length of 11 kilometers. The connection between Tholen and Zuid-Beveland created the Zoommeer, part of the Scheldt-Rhine connection that connects the port of Antwerp with the Waal. If it had not been for the Markiezaatskade , the Zoommeer would have extended to Bergen op Zoom. This dam was built between 1981 and 1983 to facilitate the construction of the Oesterdam . With the construction of the Markizaatskade, the Zoommeer became the water between the Markizaatskade and the Oesterdam . The Oesterdam runs parallel to the Markiezaatskade . From the east one sees successively the Oosterschelde, the Oesterdam, the Zoommeer, the Markiezaatskade , the Markiezaatsmeer and the coast of North Brabant.
The Tholense Gat, the water between Tholen and Noord-Beveland, was closed by prolonged spraying, which was considerably cheaper than a stone closure, whether or not by means of a cable car. As the work progressed, the opening to be closed became smaller and smaller, but the amount of water flowing back and forth remained the same, causing the flow to increase continuously. Because it seemed that the closing and raising of the last hundred meters would be a lengthy and costly task, the final closure of the dam was delayed until the Oosterscheldekering was ready. The current that arose at ebb and flow could then be temporarily turned off by lowering the gates of the barrier. The Oesterdam was finally completed in 1986.