An assessment of the suitability of the Environment Agency's water-quality classification system for use in urban catchments.

Despite the increasing range of water-quality indicators, the classification and target-setting strategy which has been adopted by the Environment Agency for England and Wales is dominated by the assessment of water chemistry at low flow. Using the example of Pymme's Brook in north London, this paper examines the suitability of such data for classifying the quality of urban watercourses and its ability to reveal quality changes. The data expose a weakness in the Environment Agency's methodology, because they suggest that, when used alone, chemical monitoring leads to water quality being greatly over-estimated and inappropriate targets being set. It is therefore recommended that other quality indicators should be fully integrated into the assessment system in order to overcome these problems.