The overall evaluation of the biological status per surface water body is based on the evaluation of the biological quality elements (BQE) : phytoplantcon, aquatic flora, macroinvertebrates an fish. In order to determine the overall evaluation of the biological status per surface water body the worst status assessed by the different biological quality elements ist retained („One out - all out“ principle).

According to the water framework directive WFD (DIR 2000/60/CE), important physico chemical parameters and river basin specific pollutants are measured in the surface water bodies for the assessment of the ecological status. The modalities for this monitoring are stated in the grand ducal Regulation of 15 January 2016 (règlement grand-ducal du 15 janvier 2016 concernant l'évaluation of the dimension d'eau de surface).

According to the water framework directive WFD (DIR 2000/60/CE), important physico chemical parameters are measured in the surface water bodies for the assessment of the ecological status. The modalities for this monitoring are stated in the grand ducal Regulation of 15 January 2016 (règlement grand-ducal du 15 janvier 2016 concernant l'évaluation of the dimension d'eau de surface). General physico-chemical parameters are used together with the river basin specific pollutants for evaluation of the ecological status.

The "good ecological potential" is the environmental quality objective defined by the water framework directive for artificial and heavily modified surface water bodies. The assessment of the ecological potential is presented in four classes ranging from 1 to 4 (good and higher, moderate, poor, bad). The classification of the ecological potential is based on the biological, physico-chemical and in some cases also the hydromorphological quality elements.

Macrophytes are a sub-element of the biological quality element (BQE) of the aquatic flora used for the assessment of the ecological status/potential. The assessment is made in 5 classes : high (blue) - good (green) - moderate (yellow) - poor (orange) - bad (red). Macrophytes are particularly sensitive to organic pollution, trophy and hydromorphology.

The chemical status of the surface water bodies is assessed as being good or failing to achieve good chemical status. The assessment of the chemical status for the third river basin management plan is based on the list of substances of directive 2008/105/EC and the environmental quality standards established by the new directive 2013/39/EC.

Phythobenthos (Diatoms) are a sub-element of the biological quality element (BQE) of the aquatic flora used for the assessment of the ecological status/potential. The assessment is made in 5 classes : high (blue) - good (green) - moderate (yellow) - poor (orange) - bad (red). The diatom assemblages are different in function of concentrations of nutrients and organic pollutants.

Macrophytes and phytobenthos (diatoms) are two sub-elements of the biological quality element (BQE) of the aquatic flora used for the assessment of the ecological status/potential. The assessment of the aquatic flora is made in 5 classes : high (blue) - good (green) - moderate (yellow) - poor (orange) - bad (red). The aquatic flora ist assessed following the sub-element the less good (worst-case).

The WFD's (2000/60/CE) quantitative status objectives aim to ensure a balance between groundwater withdrawal and recharge.

Overall evaluation of the hydromorphological status per surface water body. The assessment of the hydromorphological status is based on the mapping and the assessment of the structural quality of the Luxembourgish watercourses. The quality elements which have been covered in the framework of the structural quality mapping are: morphology, continuity and hydrological regime. The hydromorphological status is assessed in 5 classes. It is a “pessimistic assessment” because only the worst of the three parameters morphology, continuity and hydrological regime is retained.