The present invention relates to a method, arrangement and system 300 for producing or generating power, in particular electrical power, from mechanical movement caused by water flow, such as for example tidal, ocean or river currents. The system or power plant 300 comprises three main types of components, of which there are usually three or four: a framework or frame 70, at least one turbine device or turbine 350 arranged in the frame 70, and one or two (-2-) pieces of floatation devices 40, including an upper 40A and/or lower 40B floater.