Construction of hydraulic structures is considered to be one of the useful and long-term solutions to most of socio-economic problems that are faced by our societies in the 21st century. With regards to this, it is therefore necessary to constantly monitor the steady state of the dams in order to optimize the operational efficiency and safety measures for both the ecosystem and human beings. Existing methods for monitoring the state of dams are based on observing deformations dams as an independent object. The article discusses the method for estimating dam deformations in the dam-reservoir system. When conducting geodetic monitoring of dam’s displacement, it is necessary to take into account the water level in the reservoir which affects the measurement procedure and makes them more physically reasonable, taking into account the water pressure on the dam. The article shows the method of measuring the water level of the reservoir based on the construction of its 3D model.