The UK Energy Secretary Ed Davey says a 30 billion pound barrage across the Severn estuary could still be built if the right proposals were submitted.
The barrage would stretch from the Vale of Glamorgan to Somerset. Supporters believe it could provide 5% of UK electricity - but some MPs and environmental groups have opposed the plans.
MPs say developers "failed to address commercial and environmental concerns" in the barrage plan and the scheme's viability isn't proven.
Bristol Port attack barrage project, but unions champion the economic boost to South Wales.
The Prime Minister instructs ministers to explore the development of a hydroelectric barrage across the River Severn.