Power production by hydro-electric plants in response to short-term variations in the energy demand and market (hydropeaking) may lead to frequent and rapid fluctuations in flow and stage in rivers downstream of power plant outlets. We have developed a time series analysis tool designed to quantify these rapid fluctuations. They were identified by establishing river- and data-specific thresholds both for the rates of change in flow or stage, and for other peaking event parameters. In contrast to previous similar analyses, we separated peaking events into rapid increases and rapid decreases. We also analysed other parameters such as daylight conditions during peaking events, and calculated both mean and maximum rates of change in flow and stage. The results of such analysis in a Norwegian river were used to demonstrate outputs from the tool. Our tool may be useful with respect to environmental impact assessment and mitigation related to stream hydropeaking.