A floating screw turbine device with adjustable rear deflectors/diffusors is disclosed. Three pontoons, spaced apart, carry water ducts in which screw turbines are mounted. Screw turbines, mounted in a V configuration, have mirror symmetrical pitches of the screws measured over the centre of symmetry that passes through the central pontoon. Such a configuration minimizes the vibration of the device. Rear deflectors/diffusors have an adjustable pitch relative to the floors of the water ducts by which they can affect the water flow velocity through the water ducts. In one embodiment, the optimum pitch is selected according to the previously performed computational fluid dynamics simulation for the device, where the pitch is changed using hydraulic or electromechanical actuators. In another variant an artificial neural network is taught to model a global function of the system dynamics in order to achieve optimal operation.