Hydropower dams are, due to their operation on turbines and hydrodynamic effects of water continuously subjected to dynamic loading. In this paper, we present a study of structural vibrations using a laser Doppler vibrometer (LDV). Using this measuring gauge velocities are directly obtained, which is a considerable advantage to the accelerometer based measurements. Our aim is to research the impact of dynamic loading due to regular operation of dams. In Slovenia, we are increasingly faced with the problem of aging of dams. At the same time, we are also faced with changes in the environment, especially with variability in time-dependent loads such as new patterns of operation with turbines, with several starts and stops on a daily basis. The in situ structural response measurements are performed on Brežice dam. We have chosen several experimental points on the structure of the dam, where vibrations are captured on a regular basis. The LDV enables measurements of surface velocities in time domain. Since we are interested in analysis of eigen frequencies, measured data is transformed from time to frequency domain for further analysis. Investigation on Brežice dam started already during the construction and will continue in the future. With this study, we aim to present the advantages of structural vibration monitoring of the concrete used as a part of regular structural health monitoring of dams.