Petergoph, a suburb of Saint-Petersburg, was historically planned as a fountain centre similar to Versailles. The Petergoph fountain water supply system consists of artificial reservoirs formed by dams. Continued supply depends on the water level in the reservoir and the integrity of the dam. We used electrical methods for monitoring the stability of the reserve pond dam in this water supply system. Ogilvy et al. (1969) and Bogoslowsky and Ogilvy (1970a, b) used geophysical methods to investigate water leakages from reservoirs but did not use continuous observations. Their results therefore give only snapshots of the spatil distribution of dam parameters and do not characterize their temporal variation. We use two complete series of geophysical observations to monitor changes in the hydrogeological regime over a spring month, at the time of annual flood and just after.