http://www.umweltbundesamt.de/water/themen/ewr.htm

The central objective of the Water Framework Directive is the "good status" of waters in the Community. The basic thinking behind "good status" is that waters may be impaired or changed by human use, but only insofar as the ecological functions of the water are not significantly impaired. The requirements for good ecological water quality are defined in detail for the different types of waters. In addition, EU-wide minimum requirements are to be developed for some 30 priority substances on the basis of chemical quality objectives.