HELLEVOETSLUIS, OT - HELVOETSLUIS, a fortified seaport in the province of South Holland, the kingdom of Holland, on the south side of the island of Voorne-and-Putten, on the sea-arm known as the Haringvliet, 52 m.
The extensive sea-arms forming the South Holland and Zeeland archipelago are the Hont or West Scheldt, the East Scheldt, the Grevelingen (communicating with Krammer and the Volkerak) and the Haringvliet, which after being joined by the Volkerak is known as the Hollandsch Diep. These inlets were formerly of much greater extent than now, but are gradually closing up owing to the accumulation of mud deposits, and no longer have the same freedom of communication with one another.
The South Beveland (1862-1866) canal connects the East and West Scheldt; similarly in South Holland the Voorne canal unites the Haringvliet with the New Maas, which does not allow the passage of large vessels above Brielle; whilst owing to the banks and shallows in front of Hellevoetsluis the New Waterway was cut to Rotterdam.
The southern branch turns south, crosses the marsh of Biesbosch by the canalized channel of New Merwede, enters the Hollandsch Diep, and reaches the sea by the arms called Haringvliet and Krammer.