a b s t r a c tIn two survey phases (2003 and 2008) organic, nutrient and salt contamination parameters have been investigated in the lower Werra in order to estimate the importance of these different kinds of pollution for the quality component of macroinvertebrates according to the European Water Framework Directive. The chemical and biological investigations have been carried out comparing a "reference" section without salt contamination with the salt contaminated section due to the potash mining industry from Vacha to Hannoversch Münden close to the mouth of the Werra. The results show that the drastic differences between the macroinvertebrate assemblages of the Werra upstream and downstream the salt contaminated sections are clearly caused by the salt load. The other kinds of chemical impacts are not responsible for the observed fundamental change within the composition of the benthic invertebrate assemblage. General degradation of stream morphology, indicated by macroinvertebrates, shows a good ecological status for the non-salt-contaminated part of the river and a bad status for the salt contaminated sites of the lower Werra.

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This strategy paper presents a concept how to assess the ecological quality of running waters in the Federal Republic of Germany. The main cause for this paper is the original draft of an ecological guideline of the European Union (EU) which is going to become a part of a general frame guideline of the EU for waters. This guideline will ask of the European states a valuation of ecological quality of waters which is based on the undisturbed situation of the different aquatic ecosystems. The main basis for an ecological assessment is the classification of running waters in the Federal Republic of Germany according to their most important morphological and hydrological characteristics on one hand and a biocenotic description of these morphological/hydrological river types on the other hand. This method orientates itself by the natural type‐specific reference status (leitbild) of streams and rivers. The main characteristics of running waters and their leitbilds may be combined in the major complexes biology, morphology/hydrology, and chemistry. Each of these complexes can be investigated and assessed separately in a first step. In a following step, the single results may be summarized in an overall score of ecological quality. In this open assessment system (regarding the number of parameters) we propose 4 previous classes of ecological quality which may be extended later – if necessary – to 7 classes or more. Two variations of assessment are proposed. Variation 1 is thought for small to medium‐sized streams and rivers. The assessment will be necessary in an extensive blanket coverage manner, and it should be done mainly biologically. Variation 2 will consider larger rivers with predominant chemical parameters because these are investigated in nearly all these waters regularly and intensively.

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