In Austria there are 78 large reservoirs and, in most cases, they are located in nested catchments. The presence of a reservoir generally produces an attenuation effect on flood peaks downstream, however the effect of multiple reservoirs in a catchment remains unclear. The aim of this work is to analyze the combined effect of multiple dams on flood peaks along the river network at the regional scale. Its evolution is studied in space, considering how the effect changes along the river segments and as a function of the return period of the flood event. The method used consists in two steps: (i) the design hydrographs are evaluated at several locations along the river network for 30, 100 and 300 years return periods, based on interpolated flood quantiles in ungauged catchments; (ii) the peak reduction is estimated based on the information on dams in the catchment (i.e.