In a hydroelectric turbine having a rotor disposed within a stator housing, the rotor having an annular outer rim received by a channel in the stator housing, the improvement comprising a buoyant rotor, the rotor preferably having buoyancy chambers disposed within the rotor. The buoyancy chambers may be disposed within the annular outer rim, the blades or an annular inner rim, or combinations thereof. Preferably, the buoyancy chambers are filled with a material having a specific gravity of one or less, and most preferably the filler material is a polymer foam that adds rigidity to the rotor.