Campaigners say the River Severn's wildlife could suffer with the barrage
A 10-mile barrage across the river Severn could benefit wildlife in the area, one researcher has suggested.
Environmentalists fear a proposed £15bn Severn Barrage would damage the ecology of the estuary as the mudflats which some birds depend on would disappear.
Dr Robert Kirby has spent 30 years researching the estuary told BBC Wales' Week In Week Out is unique because it is Europe's most barren.
He claims the barrage would attract more wildlife.
"The system would become more bio diverse and support more species - we couldn't sustain the barrenness that we have at the moment," Mr Kirby said.
The £15bn dam from Cardiff to Weston-Super-Mare in Somerset could supply 5% of the UK's electricity within 14 years.
It could produce clean, sustainable electricity for the next 120 years, according to the Sustainable Development Commission (SDC).
In the programme, the SDC's chairman Jonathon Porritt takes a look at both sides of the argument.
"The barrage would be an enormous prize," the ex-Friends of the Earth director says.
"It would decisively mark the point where we got serious about climate change. But there is no shortage of questions.
The barrage would stretch from south Wales to the Somerset coast
"If I can't find answers it's going to be very difficult, even for someone like me, to proceed with the barrage. So it's going to be some journey."
A feasibility study on the project by the Welsh Assembly Government and UK Government was announced in January and is due to reach its conclusions at the end of the year.
The Severn estuary has 42-feet high tides, which is the second largest in the world and makes up 80% of the UK's tidal resource.
It could significantly contribute to meeting the government's renewable energy targets.
Yet environmental campaigners fear barrage electricity would be more expensive than renewable alternatives.
They also say some 14,000 hectares of saltmarsh and mudflats would be lost through the building of a large barrage, resulting in the loss of migratory birds that nest there.
It would also hit the fish populations of the Severn, Wye and Usk rivers, which all flow into the estuary above the point where the dam would be built.
But with the threat of global warming looming, Jonathon Porritt examines whether any concerns about the barrage would be enough to stop it going ahead.
Week In Week Out, Tuesday, 14 October, BBC One Wales, 2235 BST.