The design of hydropower is determined by estimates and long-term forecasts. These forecasts and estimates are highly uncertain and make performance evaluation and design choices challenging. Effective values deviating from the estimates can have a significant impact on the success of a hydropower project. Furthermore, if ongoing research should improve the accuracy of these long-term forecasts, such as climate change projections and electricity price forecasts, a high uncertainty will remain and finally lead to a demand for adequate design methods that incorporate these uncertainties into the planning process. Various design methods have been developed which allow for management of uncertainties. The Information-Gap Decision Theory (IGDT) was suggested as a potential approach to deal with climate change uncertainties. In this study, the IGDT was formulated and applied first time to a real hydropower project. Beside the identification of the values and limitations of IGDT specifically for hydropower sector, the study is intended to provide a basis for the application of the method in the engineering practice.