As a result of its mountainous nature, many hydroelectric power stations in the Black Sea region are constructed on rock slopes that require a high degree of engineering. Serious negative impacts related to construction safety, such as slope instabilities, that make the risk encountered excessive have also been experienced during the construction and operation stages of these plants. In this study, the mechanism of a slope instability, which occurred in the area of a stream-type hydroelectric power plant and threatened its loading pool and power house, and triggering factors were investigated and the applicability of some remedial measures were assessed. An assessment of the geological and engineering data from the study site indicated that the instability has developed in a certain part of the slope cut along the bedding plane in a sedimentary sequence, where the dip directions of the slope and bedding planes coincide. The back-analysis of the instability proved that the residual shear strength of the bedding planes was a critical factor. A series of analyses conducted along different slope profiles indicated that the most critical mode of failure in the study site would be planar failure, while circular failures through the rock mass and colluvial deposits are not anticipated. Some remedial measures, such as slope flattening, the use of rock bolts, and slope rotation, were also assessed based on preliminary analyses.