The construction of the Brouwers Lock in 1978 reconnected Lake Grevelingen with the North Sea. This turned Lake Grevelingen into a saltwater lake.
The water regained some of its former salinity, and many sea animals gradually returned. As a result, the underwater life forms in the lake are currently flourishing. Between the water plants and the stones hide schools of small fish, like the black goby that is a favourite food of many fish-eating birds. The lake has a wide variety of sea anemones and shellfish, such as the slipper limpet, schools of haring, butterfish and eels. After research into the effects of the saltwater environment, it was decided in 1986 that Lake Grevelingen would permanently remain a saltwater lake. In cooperation with the Department of Public Works, a new water management plan was drawn up in 1999. The lock in the Brouwers Dam is now open year round, except for 30 days between September and December. This allows the lake water to be refreshed more effectively and enables the fish to pass between the lake and the sea as much as possible. Nowadays, Lake Grevelingen is one of the cleanest and clearest saltwater lakes in Southwest Europe.