A water powered turbine (1) comprises a main support frame-work (2) which rotatably carries a rotor (3) comprising a main shaft (5) to which three blades (7) are attached by carrier discs (8) and (9). The carrier discs (8, 9) are rigidly secured to the main shaft (5), and the blades (7) are pivotally connected to the discs (8) and (9) by pivot shafts (16) and (17). Each blade (7) is of constant hydro-foil cross-section along its entire length and defines a first upper spiral (12) and a second lower spiral (13). The first spiral (12) extends from a first end (10) which is coupled to the main shaft (5) by the carrier disc (8), and the second spiral (13) of each blade (7) extends from a second end (11) of the blade (7) which is coupled to the main shaft (5) by the carrier disc (9). The first and second spirals (12) and (13) are of opposite hand and extend from the respective first and second ends (10, 11) to meet midway between the respective first and second ends (10, 11). The first and second spirals (12, 13) define respective central spiral axes which substantially coincide with a main central rotational axis (4) about which the rotor (3) is rotatable. The pivot shafts (16, 17) of each blade (7) define a corresponding secondary axis (18) about which the blades (7) are pivotal for selectively altering the dive angle of the first and second spirals (12) and (13) of the blades (7).