CONSERVATIONISTS have hit out at plans to build a 10-mile concrete barrage across the Severn estuary to generate renewable power.

A handful of schemes are being considered by the Government for the estuary, which has enough power locked within its tides to generate 5 per cent of the UK's energy needs. If a tidal scheme came to pass, it would be the world's largest-ever green energy project.

In January, Energy Secretary Ed Miliband announced a shortlist of five advanced schemes which had met the Government's criteria, including a controversial barrage from Cardiff to Weston-super-Mare. Ahead of the announcement of the finalised shortlist, the Wildfowl & Wetlands Trust (WWT), the Wildlife Trusts, the Royal Society for the Protection of Birds (RSPB) and the Wye and Usk Foundation have said they are concerned that a barrage risks "destroying the estuary in its wake".

Andre Farrar, of the RSPB, said: "Climate change will bring change to the estuary, as it will every low-lying coast of the world.

"We have two choices: you can allow the environment and its wildlife to adapt, whilst harnessing renewable energy from the estuary in a sustainable manner – or you can build a 10m high barrage from Cardiff to Weston, destroying the estuary in its wake.

"The challenge is to harness the much-needed power of the Severn's tide and avoid destroying the nature of the estuary – Government has a chance to show real leadership and put the UK at the forefront of tidal power technology."

A meeting took place at the Wildfowl & Wetlands Trust at Slimbridge, near Dursley in Gloucestershire, where the landscapes and wildlife of the Severn estuary inspired founder Sir Peter Scott. Opponents fear for the inter-tidal habitats, fish such as the shad, European eel and salmon, and migratory birds such as the 7,000 geese which descend on the muddy banks each year.

WWT chief executive Martin Spray said: "Following Peter Scott's example, we're using this special place to inspire these influential people to make the right decisions for the future of the Severn.

"We're all aware of the difficult choices ahead of us. Now is the time to quantify the value of the Severn, think clever and keep the Severn working as a fully functioning ecosystem."

The Department of Energy and Climate Change is expected to confirm the shortlist early next month. Dr Stephen Marsh-Smith, chief executive officer of the Wye & Usk Foundation, said: "The flocks of waders and wildfowl that can be seen in winter are an obvious sign of the international importance of the Severn for conservation.

"Unseen by many are the riches beneath the water. Salmon, eels, shad and lamprey would become extinct if an inappropriate technology is chosen and, with their loss, a whole rural economy would disappear."

Half-a-million pounds of public money has been ring-fenced for two other unproven schemes – a "reef" and a "fence". The tidal "reef", brainchild of Cornishman Rupert Armstrong-Evans, is the only Severn energy proposition to have secured the full backing of the environmental lobby, and has been given the thumbs-up by engineering experts Atkins.

Joan Edwards, head of living seas at the Wildlife Trusts, said: "The Severn Estuary is one of the UK's incredible and unique ecosystems, which will become even more important as species have to adapt to climate change.

"If there are options which offer us the ability to harness the power of the Severn's tidal range, with minimal impact upon the ecosystem, we have both a moral and ethical obligation to ensure these are pursued."