Water-powered electricity generating apparatus, for use in rivers and other bodies of water having current flow therein, comprises a water wheel and an adjacent platform. The water wheel has a number of blades which are pivotally attached adjacent a first end thereof to vertical rods which extend between the top and bottom of the water wheel. A controllable stop, movable between an upper position in which it may contact a second end of the blade, and a lower position in which contact with the blade is not possible, is provided for each blade. The wheel also comprises a drive gear having downwardly-facing teeth. The drive gear meshes with gears of dynamos carried on the platform adjacent the water wheel.The apparatus is placed in a river or other body of water having current therein. When traveling in an upstream direction, the blades swing freely parallel to the current. When traveling in a downstream direction, the second ends of the blades rest against the stops, and the blade presents a surface against which the current acts to turn the wheel. The wheel, powered by the blades in contact with the stops, and unhindered by the other blades, rotates continuously in one direction. Rotation of the wheel causes the drive gear to rotate, which causes the dynamo gears to rotate causing the dynamos to produce electricity.