Ecomare

The majority of the delta waters used to be brackish. Due to the delta Works, many of these areas have become fresh or salty. The Veerse Meer, Lake Grevelingen and sections of the Westerschelde are still brackish, while the Oosterschelde and the Haringvliet are not. In South Holland, the brackish areas are limited to grounds on the landward side of the dikes by Goeree Overflakkee, Voorne, Putten, and in the Hoeksche Waard. Brabant has a few brackish water areas on its border with Zeeland. The Biesbosch used to be brackish. In North Holland, brackish water can be found behind the Hondsbossche Zeewering (sea wall), in the Wieringermeer and on Texel. The rest of the Wadden Islands, Friesland and Groningen have a few inland brackish water areas. The Dollard is a large offshore brackish water area. The Zuiderzee used to be one large brackish water region.

At a workshop on 17 September 1997, the RIKZ presented a study of the possibilities for extending brackish water areas in the Netherlands. This was a follow-up from the report 'Tussen Zilt en Zoet' ("Between Silt and Fresh"). All of those present agreed that extension of the area is desirable in view of enriching nature in the Dutch coastal areas. The report did not designate any places where this should occur. However, a discussion has begun as to whether or not the area should be extended within the borders of the present tidal flat region, or should it be seen as an extension of the tidal flat region at the cost of present cultured land. This discussion is being conducted mostly via the Interwad site on Internet.
A simultaneous discussion is going on concerning the question of whether or not the fresh-saline transition between the Oosterschelde and the Krammer-Volkerak should be dealt with. Since the construction of the Volkerak (1969), the Oester and the Philips dams (1987), no water from the Maas and Rijn can enter the Oosterschelde. This was done purposely at the time to protect the region from the strongly contaminated river water. The Oosterschelde, however, changed from a river mouth (with a gradual change from fresh via brackish to saline water) to a permanently salty sea arm. Research and model studies from 1998 by the RIKZ and the RIVO showed that the natural quality and productivity of the Oosterschelde would significantly advance if there was a renewed flow of fresh water. Some of the typical marine species would disappear from the brackish section, however the majority of the existing fauna, including the shellfish stock, would be preserved. One expects that the eelgrass fields would return, and with a greater supply of nutrients, an increase in the amount of shellfish and zooplankton. The function as nursery for juvenile fish would also be strengthened.
One problem with an eventual increased flow of fresh water into the Oosterschelde is the quality of the Maas and Rijn water. This is still so bad that it would be irresponsible to permit additional river water in from the Volkerakmeer (via the Zoommeer) or from the even more polluted Hollands Diep. In addition, the Volkerakmeer has too little water for this purpose.

In order to be able to survive in brackish water, a species must be tolerant to saline conditions as well as fresh water. There are not many species capable of that. Amphipods and common prawns can live in varying saline concentrations. Some kinds of water bugs and amphipods can live in conditions if they are not too saline. Characteristic plants are horned pondweed, brackish water crowfoot, beaked tasselweed and spiral tasselweed.