There is provided a turbine for a hydroelectric power installation. The turbine has a rotor with a plurality of blades, with the rotor being arranged in front of a guide apparatus (in the flow direction). The pitch angle of the blades of the rotor is adapted to be variable. As the rotor is arranged in front of the guide apparatus (in the flow direction) the flow meets the rotor first and only thereafter meets the guide apparatus, thus affording optimum flow conditions for the rotor.