Macro and micro hydropower systems are described, along with a consideration of the technical and environmental problems involved. A case study, with Bargoed in the Rhymney Valley, South Wales as the proposed site is then presented, with some of the issues involved when choosing a specific hydropower-harnessing scheme discussed. In conclusion, a set of associated proposals, which would improve the Rhymney Valley in an environmentally-and socially-beneficial way, are described.