Geophysical exploration methods can be valuable for the investigation of filled storage reservoirs. Impressed current circuits or natural ground potentials are analyzed for this purpose. General structural data are obtained from horizontal resistivity profiles. Ground bed details and seepage zones can be located by means of underwater equipotential surveys. Salinity and temperature measurements serve for the hydrological investigation of submerged springs and streams in natural lakes. The proposed interpretation methods can be readily adapted to specific local conditions.