The output of monitoring programmes such as the National Aquatic Ecosystem Biomonitoring Programme must be used in the management of aquatic ecosystems. To achieve this, collected data must, through a systematic framework, be linked to measurable management objectives. This paper demonstrates how the results obtained with biological indices and system-specific knowledge, are combined to derive semi-quantitative assessments of ecosystem condition. These assessments provide the basis for responding to the results of a river monitoring programme.