Assessment of the ecological value of streams and rivers is important to determine which watercourses should be preserved for the future. Throughout the world, a large number of evaluation systems have been developed either to assess complete river systems or merely to evaluate the water quality.

However, in a region such as Flanders, where rivers are generally very polluted, it is not only important to evaluate the current ecological value, but also to recognize those watercourses which still have a high potential value. For this purpose a system was developed in Flanders to assess the present as well as the potential ecological value of streams and rivers. The evaluation is based on a number of morphological characteristics, on the water quality and on the aquatic communities. The result is a global ecological evaluation map of each river basin. This map is made available to policy makers in order to assist in the elaboration of purification programmes and river restoration and conservation projects.