A system for producing hydrogen from water, making use of a stream of water such as a gulf stream or tidal stream, includes a number of submerged modules, each having a turbine that can be driven by the stream of water. The turbine is coupled to a generator for generating electrical energy. Each module may have submerged decomposition means for decomposing water into hydrogen and oxygen using the electrical energy generated. The modules are provided with means to control the depth of the modules below water level, and furthermore with means for automatically orienting the front of the modules--viewed in the longitudinal direction of the turbines--to the direction of flow of the water or an angular position deviating therefrom.