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  In the present state of the rivers of NRW, we can point to a number of “ecological bottlenecks” that need to be dealt with if we are to recover intact waterways in a state approximating to the natural. The most important points are as follows:

  • Making it possible for fish to migrate from the rivulet to the sea (both upstream and downstream)
    Our waterways today are marked by a great many barrage constructions (weirs, dams etc.) which restrict the migration of fish and other aquatic species. Besides upstream migration, the successful downstream migration of fish is hindered or disrupted above all by unprotected hydropower stations with their turbines. As the effect of these constructions is cumulative from the rivulet down to the sea, and as there are several thousand weirs on NRW’s waterways, a systematic approach to the recreation of a migratory passage for fish is indispensable. Here the success rates or survival rates of the different fish populations, when migrating upstream or downstream and negotiating the entire chain of barrages and similar constructions are the important target variables for all the measures for improvement that have been envisaged.

  • Improvement of waterscapes (quality of habitat)
    River development has led to the far-reaching loss of natural waterscapes and watermeadow areas. Straightening measures, development of the banks and riverbed, changes to the catchment area and the building of embankments have all had severe detrimental effects on the form of the waterways and accelerated the downflow process. Moreover, in connection with ongoing water maintenance natural structures (like large woody debris, for instance) get removed from the river.
    It has now come to be recognised that such changes not only bring considerable problems from the point of view of Nature – they also cause difficulties when it comes to protecting the human population against floods. The recreation of natural stretches of river with plentiful variety of structure, intact watermeadow zones and green bordering areas (buffer zones) will restore the quality of the habitat to the benefit of the natural fauna, as well as protecting human beings against floods caused by an artificially accelerated downflow.

  • Recreation of spawning grounds (water quality, protection of the catchment areas)
    The high density of population and intensive use of the land for farming in NRW has led to an excessive contamination of the waters with nutrients. Even if in many places water quality Class II has been achieved, the spawning grounds in most upper reaches (the grayling and trout regions) are today suffering from nutrient contamination and an excess of fine sediments that drain into the river. The interstitial spaces in the gravel beds get blocked as a result, and the oxygen content in the water deteriorates. This is a highly critical situation for species that need gravel to spawn (like salmon, trout and grayling), as the eggs remain on (in?? Eier liegen im Kies) the gravel bed for some time and are dependent on a powerful flow of water rich in oxygen. In addition, the increased growth of algae in the water gives rise to artificially high pH levels (> 9), which are likewise critical for fish and other organisms. In salmonid spawning grounds protective measures are therefore needed in the water catchment area (involving border zones and the sparing use of land areas), as well as improvements in waste water technology (e.g. the retention of mixed effluents).

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