The article regards the movement of the negative and positive release waves from the reservoir on the Oredezh River. There was a model of unsteady water motion used for calculation the spread of the release wave. The release was conducted on 06/19/2017 and consisted of three phases. In the first phase, the gate was closed and the water discharge fell from 3.6 to 2.5 m3/s. An hour later the gate was raised and during a half an hour water was released with an average flow rate of 4.2 m3/s. There were 7 points organized to monitor the dynamics of water levels in the river. They were located at a distance of 91.5 to 2443 m from the dam. The observation interval was 1 minute on most targets. There is advisable to use a one-dimensional model of unsteady water motion (Saint-Venant equation) for calculating small release waves of slowly changing unsteady water motion in cases where topographic materials are available. This allows to determine the stream features over the whole considered river extension. The system o