A geophysical survey using electrical resistivity tomography (ERT) method(25 ERT profiles of 240m total length and 2 ERT profiles of 1000m total length) in the area of Plati River valley gave valuable information regarding the stratigraphy, related to loose sediments, various faces of flysch and limestone, the tectonic status and the detection of areas of thick and extensive sheared siltstone, that geoelectrically is similar to clay,material useful for the core of the future dam. Both branches of river and valley and in greater detail the area near the position of the dam have detected showing the underground in a 2D and 3D manner. The thickness of neogene andflysch exceeds 40m. Alternations of siltstones-sandstones are met in flysch and in places cohesive sandstones are also met without continuation in an extended area. The siltstonelayers due to their shear character present clayey characteristics in respect of their resistivities. In general zones of limestone uplift have not been detected, which may create problems of leakages apart of the dam area where lateral inhomogeneity between flysch and limestone has been detected (probable fault). The various limestone bodies met in flysch or neogene do not have continuation in depth and they are isolated.