Abstract: A generating apparatus for generating electrical power from a horizontal water flow comprises a fixed hub on a support structure and a power wheel arranged for rotation about a vertical axis about the hub. The power wheel includes rotor vanes adapted to cause rotation of the power wheel when the power wheel is subject to a substantially horizontal water flow. One or more generators are provided on the hub to produce electrical power output from rotation of the power wheel relative to the hub. A shroud is rotationally mounted on the hub and arranged to cover at least some of the rotor vanes of the power wheel, so that the water flow is concentrated on the rotor vanes on one side only of the power wheel. A directional controller holds the shroud in a predetermined rotational position relative to the hub dependent on the direction of the water flow.