Tidal stream is a different technology to tidal range, such as that being considered for the UK's Severn Estuary, which uses conventional water-driven turbines to exploit the rise and fall of estuary tides. Uncertainties over the best generating-system design and challenges over installation, maintenance and transmission connection still exist, but tidal stream is generating attention since it may, in the long term, be cheaper to install and maintain, and may have less impact on the environment.