Considering the implementation of the Water Framework Directive, the assessment of large rivers remains an open question and this topic will be only covered during the last stage of the Intercalibration exercice (till 2011-2012). In addition to a necessary evaluation of the good ecological status based on hydromophological criteria, fish, and probably macrophytes, appear to be the most appropriate biological quality elements for large river. The first aspect is related to the definition of a large river, in terms of size (river width, water depth,) but also in relation with the water bodies of the floodplain itself. The second point is related to the feasibility of a biological assessment on both the main channel and the lateral water bodies. Is it possible to use a standardized sampling method for the different habitats? In addition, there is clearly a need to develop specific metrics, based on a comprehensive analysis of species strategies (including lateral/longitudinal migration) and considering both lotic and lentic habitat characteristics and their associated species. Finally, most of large rivers are classified as heavily modified water bodies and the definition of the Good Ecological Potential has also to be considered.