The Grevelingen (now the Grevelingenmeer), located between the islands of Goeree-Overflakkee and Schouwen-Duiveland on the border of the provinces of South Holland and Zeeland, is a former estuary of the North Sea . As part of the Delta Works, the sea arm, the Brouwershavense gat, was closed off from the sea in 1965 by the Grevelingen dam and in 1971 by the Brouwers dam , thus becoming the largest saltwater lake in Western Europe. The Grevelingenmeer is mainly used by water sports enthusiasts and other recreationists. The salinity of the Grevelingenmeer is maintained by the Brouwers lock, a seawater passage lock in the Brouwersdam .

An area with an area of 13,872 hectares has been designated as a protected Natura 2000 area.