As from today, the Haringvliet sluices can be set ajar in order to allow migratory fish from the North Sea to swim into lake Haringvliet. A decree has been adopted to partially open the sluices when sufficient fresh river water is entering lake Haringvliet. The area remains an important source of fresh water for the drinking water and agriculture sectors. For that reason, several measures have been taken to combat salt water intrusion and keep up freshwater supplies.
Today, Minister Cora van Nieuwenhuizen (Infrastructure and Water Management) officially adopted the Sluices Ajar Decree, exactly 47 years after the Haringvliet sluices were rendered operative. ‘We are still experiencing a drought in the Netherlands, so it will be a while before the sluices are actually opened,’ the Minister stated. ‘They will only be set ajar, in a controlled manner, when this does not impact freshwater volumes. Extensive measurements will teach us how the water behaves. If we find that too much saline water is entering lake Haringvliet, the sluices will be closed.’
International fish migration
Because of the drought that has affected the Netherlands over the past few months and the low river discharge, the sluices will remain closed on 15 November. Once river discharges are sufficiently high, Rijkswaterstaat can gradually start setting sluices ajar. By regularly setting the Haringvliet sluices ajar, migratory fish such as salmon and sea trout are free to swim into lake Haringvliet and the rivers beyond to spawn. The “Rhine Riparian States”, among which the Netherlands, have been collaborating for years on removing barriers for fish. In addition, letting in saline water will improve the biodiversity of Haringvliet water, while also opening up opportunities for new nature development.
Rijkswaterstaat, the Hollandse Delta district water board, and Evides Water Company will together ensure that the freshwater balance in the region is kept up to par. This will safeguard an adequate supply of drinking and agricultural water. Leaving the sluices ajar will increase the salinity in the western part of lake Haringvliet. This is why the Sluices Ajar Decree stipulates that the water east of the Middelharnis–Spui line will remain fresh. Over the past four years, the Hollandse Delta water board and Evides Water Company have constructed several new inlets, pipes, ditches, and canals. The freshwater supply to the islands of Voorne-Putten, Goeree-Overflakkee, and Schouwen-Duiveland has thus been secured and everything has been prepared for a careful start by leaving the sluices ajar.
Rijkswaterstaat has initiated a comprehensive research and monitoring process to carefully monitor whether salt intrusion is not passing the stipulated boundary. Furthermore, the Hollandse Delta water board and Evides Water Company are monitoring the freshwater inlets.