The aim of the study was to assess the impact of the building of hydroelectric dams along the Rhône River in France in the first instance and to evaluate the effect on aquatic communities, especially fish communities, of the increase of minimum flow in by-passed sections. Fish were collected using Electric fishing in independent habitat units (Nelva et al., 1979, Vadas and Orth, 1993). Data were collected between July and December form 1985 to 2020. The dataset includes the number of individuals sampled for each species in one station during one sampling campaign (once a year). The sampling area is indicated. See example of publication using the data : Cauvy-Fraunié, S., Trenkel, V.M., Daufresne, M., Maire, A., Capra, H., Olivier, J.M., Lobry, J., Cazelles, B., Lamouroux, N., 2020 -Interpretation of interannual variability in long-term aquatic ecological surveys. Canadian Journal of Fisheries and Aquatic Sciences, 77(5): 894-903. https://doi.org/10.1139/cjfas-2019-0146