The aim of this study is to predict the possible changes in runoff from Lake Onego catchment using the three largest tributaries Shuya, Suna and Vodla as a case study for assessing expected climate change in the 21st century in accordance with the greenhouse gas emission scenarios RCP 2.6 and RCP 8.5 – the best and the worst in terms of environmental impact, respectively. Information about the change in meteorological elements required for runoff calculations was obtained on the basis of the climate models MPI-ESM-MR and IPSL-CM5A. To assess the possible change in runoff as a result of changes in the regional climate, the runoff model ILHM was used. When both climate models are applied, a significant increase in air temperature in the RCP 8.5 scenario leads to an increase in the estimated values of evaporation, which largely compensates for the increase in river runoff due to increased precipitation. In the RCP 2.6 scenario, there are no significant changes in evaporation. A combination of RCP 2.6 and MPI-ESM-MR produces a slight decrease in runoff by the end of the 21st century. It can be assumed that the change in runoff from the catchment of Lake Onego will be in the interval between the estimates made in the two extreme scenarios and one should not expect extreme changes in the hydrological regime of rivers in this region.