The development of biological assessment methods in The Netherlands in the past decades is described. National and regional water management policy has amplified the need for ecological assessment methods. These are being developed for five individual water types: running waters, ditches, sand, clay and gravel pits, canals, lakes and ponds. The running water project is described in more detail. This concerns the running waters of the higher, mostly Pleistocene grounds, especially in the east and south of The Netherlands. Data are analysed using multivariate analysis, clusterprogrammes and ordination techniques. Examples are given of the method used to formulate a national typological classification of the Dutch running waters, based on the master factors found through the data analyses, combined with additional ecological literature data. Regional specification and detailing will follow as a next step.