There could actually be conservational benefits to the Tidal power generators too though. All they basically do is delay the tide a few hours in and out.
http://www.severntidal.com/info.html
The small difference in level also facilitates the safe passage of salmon and other fish species through the special turbines, something that is not possible with conventional turbines with their high pressure drop and sharp edged high-speed runners (rotors). There is nothing to suggest that there should be any more risk (possibly less) from a salmon passing through a turbine than from ascending a natural obstacle of similar height in a river such as a set of rapids, with sharp rocks and high turbulence.
RIP Dad 25/11/51 - 13/12/13. You will be missed but never forgotten.
