The Brouwersdam, a dike connecting the two islands on the west, closes off the Grevelingen from the North Sea.

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, partially restoring and maintaining the saline character of the Grevelingen.

Benthic life (mussels, oysters and many fixed organisms) is rich in the shallow waters in the photic zone, but the deep sediments are less conducive to marine life, and fishes in open water are rarely observed during diving.

Brouwerssluis is the home of a seal colony subsisting on fish transported by the seawater stream entering the water body during high tide.