Changes on river flow regimes downstream of reservoirs or multireservoir systems located in the Central Pyrenees (between Aragón river and Noguera Pallaresa river) is studied. The reservoir management aims to store water during a part of the year in order to release relatively high flows for agricultural or hydropower purposes. A high variability in the intensity of the fluvial regime change and in the seasonality of the released discharges has been observed. The impounded ratio index, the aim of the reservoir and the location of the reservoir into the multireservoir system explain most of the observed variance in the study area.