WARNING: SOME ERRORS WHERE SPOTED WITHIN THE DATASET. USE IS NOT RECOMMENDED BEFORE 2018 UPDATE. This occurrence dataset countains fresh water fish occurrences in wallonia (Belgium) compiled by Hydrobiology unit at the Department of Study of the Natural and Agricultural Environment (DEMNA- Public Service of Wallonia). The data come from an ongoing monitoring network on the biological quality of water bodies in Wallonia, and previous/alternative samplings events performed by DEMNA's hydrobiology unit. Opportunistic observations made during non-fish-target activities has also been included into the dataset. The Current monitoring network is composed of more than 440 sites, distributed among small streams to the largest rivers/canals from the hydrographic districts of the Meuse, the Scheldt, the Rhine and the Seine. The network was set up in order to perform the biological monitoring of water courses (Fishes, diatoms - doi:10.15468/vvkk9a -, macroinvertebrates - doi:10.15468/ew00u8 - and macrphytes- ...