The Haringvliet is a large inlet of the North Sea, in the province of South Holland in the Netherlands. It is an important estuary of the Rhine-Meuse delta. Near Numansdorp, the Hollands Diep splits into the Haringvliet and the Volkerak estuaries. It is closed off near Goedereede from the North Sea by the Haringvlietdam, which provides a road connection between the island of Voorne to the north and the island of Goeree-Overflakkee to the south. The dam with its sluices was built as part of the Delta Works sea barrier protection works, and allow for a brackish ecological environment.