EC - Water Framework Directive - WFD - 2000/60/EC -Annex V - Classification of surface - and groundwater status -Annex V - 1.Surface water status -Annex V - 1.4. Classification and presentation of ecological status -
WFD - Annex V - 1.4.1. Comparability of biological monitoring results
Member States shall establish monitoring systems for the purpose of estimating the values of the biological quality elements specified for each surface water category or for heavily modified and artificial bodies of surface water. In order to ensure comparability of such monitoring systems, the results of the systems operated by each Member State shall be expressed as ecological quality ratios for the purposes of classification of ecological status. The procedure of the intercalibration exercise is outlined in this section.
(see Annex V 1.4.1. Comparability of biological monitoring results - L327/58)