Swansea Bay's tidal lagoon could power 120,000 homes for 120 years
7 February 2014 Last updated at 07:44 GMT
A £850m tidal lagoon in Swansea Bay could provide power for 120,000 homes for 120 years.
Tidal Lagoon Swansea Bay Ltd says it is the first step towards developing technology that could meet 10% of the UK's electricity needs from the tides.
The six-mile-long U-shaped seawall will go from Swansea docks to near Swansea University's new Fabian Way campus.
It would take two years to build and create 1,850 construction jobs.
Environment correspondent Iolo ap Dafydd reports.