Urban aquatic habitats, which are often greatly impacted, may be classified according
to the WFD as a separate class of the so-called ‘heavily modified water bodies’ (i.e.,
surface water bodies, which as a result of physical alterations by human activities are
substantially changed in their character) or even as ‘artificial water bodies’ (surface water bodies created by human activities). They very often cannot be restored to the highest quality and achieve ‘good ecological status’. In that case, the WFD recommends using the concept of Maximum or Good Ecological Potential (MEP/GEP), which is defined as the potential for the development of chemical, physical and biological processes within realistic boundaries. The quality elements applicable to artificial and heavily modified surface water bodies shall be those applicable to whichever of the four natural surface water categories discussed in the WFD most closely resembles the heavily modified or artificial water body concerned.