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Grevelingen Lake was created in 1971 when the Grevelingendam and Brouwersdam closed off the Grevelingen estuary from the North Sea as part of the Delta Works flood protection programme. The trapped seawater remained, creating Europe's largest saltwater lake at approximately 110 square kilometres. Limited water exchange through a sluice maintains salinity but eliminates tidal currents. The lake has developed its own unique marine ecosystem over fifty years, with species adapted to the stable conditions that differ from the open Oosterschelde estuary nearby.

Grevelingen is one of the best beginner dive locations in Northern Europe. The absence of tidal currents eliminates the timing constraints and current risks present at coastal sites like the Zeelandbrug. Multiple shore entry points with gentle slopes allow easy access. Maximum depth at most dive sites is 15 to 24 metres, and many sites have interesting features at 5 to 10 metres. The lake is popular for training dives, try-dives, and building experience before venturing to tidal sites.

A drysuit is standard for Grevelingen diving year-round, as water temperatures range from 4 degrees in winter to 20 degrees at the surface in late summer. Below the thermocline at roughly 8 to 12 metres, temperatures can be significantly colder than at the surface. Full drysuit training is recommended before visiting, though many dive schools at the lake offer drysuit courses. In summer, a thick wetsuit of 7mm is usable for shorter dives, but comfort is significantly better in a drysuit.