Full recolonization, however, is a distant goal. Soil erosion in the catchment remains a threat and can easily contaminate waters with agricultural chemicals. But even here there are some hopeful signs. The European Union s policy of setting aside agricultural land is now encouraging landowners and local communities to restore landscapes for uses other than farming. And on the Sieg, for example, legislation has helped to create a diversity of habitats along the river banks.
Further plans exist to restore parts of the river channel to support fish and wildlife.
A key factor in this is that people s thinking has changed, says Marmulla. They are now more ecologically minded and this helps to keep pressure on the planners and local authorities to increase efforts in favour of better environmental management. But there is much work to do and some European waters may never fully recover. Still, there may be some lessons for developing countries, such as China and India, where the damming of rivers has hit fish stocks. Many developing countries are trying to come to grips with habitat degradation and increasing pollution.