A flowing-water driveable turbine assembly (104) for location in river or sea areas with unidirectional and bidirectional water flows. The turbine assembly comprises a turbine support (106) with positive buoyancy in water. The turbine support (106) is arranged to be anchored by an anchoring system (108) to a water bed. The turbine assembly comprises at least one turbine (110). The positive buoyancy of the turbine assembly in water has an upward force to constrain the turbine support 106 and the at least one turbine (110) to a position of floating equilibrium against a downward force of the anchoring system (108). The turbine assembly may have variable buoyancy, a duct around each turbine for directing water through the turbine to generate power from water flow, and a winch or winches for submerging the turbine assembly or parts thereof.