A control system for a hydroelectric power plant of the run-of-river type wherein the load on the turbine-generator units is matched to the flow of the river so that the units operate at the maximum head available for existing flow conditions to produce the maximum energy available from the river flow for the installed capacity of the plant and within the allowable, safe operating capability range of the turbine-generator units. Reservoir water level sensors provide a signals indicative of changing water level, sensors for generator electrical and thermal operating characteristics provide a signals related thereto, and a control connected to the water level sensors, to the generator sensors and to the turbine governor adjusts the turbine flow control devices to change the turbine power in response to changing river level within the safe and allowable operating range of the generator. Adjusting the turbine power to match the water available either when the reservoir level increases or decreases maintains maximum head for the power plant to obtain maximum energy therefrom. A tailwater level sensor and cavitation control also control the turbine flow control devices in an appropriate manner when a condition of cavitation is being approached. The control system typically is employed with a plurality of turbine-generator units in a hydroelectric power plant.