An installation for converting hydraulic energy into electrical energy, which installation comprises a hydraulic turbine, a feed duct for feeding a forced flow of water to the turbine, a discharge duct for removing the flow exiting from the turbine, and guide fins for guiding the flow through the discharge duct, said installation being characterized in that each guide fin is mounted to pivot in rotation about an axis that intersects the wall of the discharge duct, in that the installation is provided with means for controlling the angular position of the fin about its pivot axis, in that each pivotally moving fin is retractable into the wall of the discharge duct, and in that the installation is provided with means suitable for adjusting the extent to which the fin is retracted into the wall.