Grevelingen

Grevelingen or Grevelingenmeer (Lake Grevelingen) is a closed off part of the Rhine-Meuse estuary on the border of the Dutch provinces of South Holland and Zeeland.
It is situated between the islands of Goeree-Overflakkee (South Holland) and Schouwen-Duiveland (Zeeland) and was closed off as part of the Delta Works, a huge engineering project designed to protect the southwestern part of the Netherlands from flooding. The Brouwersdam, a dike connecting the two islands on the west, closes off the Grevelingen from the North Sea. The Grevelingendam, the dike on the east, blocks the inflow of Rhine and Meuse water. 
Since its closure in 1971 the saltwater of the Grevelingen slowly started to become brackish due to rainwater and excess polderwater from the islands, but the Dutch changed their mind and decided that they wanted to preserve the saline biotope. Therefore, in 1978 a sluice was created under the Brouwersdam, restoring and maintaining the saline character of the Grevelingen. The Brouwerssluis is open all year round except during storm floods.
Connexxion bus service 104 crosses the Brouwersdam, bus service 133 (and others) the Grevelingendam.
The Grevelingenmeer is the largest saltwater lake in Europe and is a popular place for holidays and water sports.
Trivia.
Professional freestyle windsurfer Steven Van Broeckhoven refers to the Grevelingenmeer as his homespot.