The Haringvlietdam bridges 4.5 kilometers of water between Goerree-Overflakkee and Voorne-Putte. The dam was completed in 1971. Apart from the Oosterscheldekering , the construction of the Haringvlietdam took the most time: 14 years. The Haringvlietdam had two functions: firstly, the dam was to protect against a future flood disaster and secondly, the dam was to discharge Rhine and Maas water to the North Sea . A closed dam would therefore not suffice. The dam has seventeen openings that regulate the amount of water that flows through the new Waterway to the North Sea . If the water levels in the vicinity of Rotterdamrisk of getting too high, the sluices can discharge extra river water into the sea. In addition to the sluices, a lock for shipping was also built. The cable car method was used to seal the rest of the hole. To spare nature special tunnels were made in a number of pillars; fish can use it to swim from the Haringvliet to the North Sea (and vice versa), even when all locks are closed.