ENVIRONMENTAL groups determined to protect the Severn’s unique wildlife have warned against going ahead with new barrage plans without carrying out extensive scientific research first.

In 2010, a government study into the feasibility of building a barrage across the river found that the impacts of a conventional high-head barrage could be catastrophic and lead to the local extinction of some species of fish and an increase in flood risk.

Following the report the £34.3 billion development between Cardiff and Weston was abandoned, to the disappointment of the scheme's supporters who had championed the need to harness the river’s power to produce renewable energy.

Despite the plans being ruled out, Corlan Hafren, a consortium established to spearhead the project carried on with its work. It is now hoping, backed by MP Peter Hain, to press on with the scheme through private investment.

But concerned non-governmental organisations and angling groups have demanded that thorough surveys and independent studies be undertaken to fully assess the harm to the Severn’s 100 fish species and 69,000-strong bird population before the consortium is allowed to go any further.

Mark Lloyd, chief executive of the Angling Trust, said: "The proposed barrage could block safe access for salmon, shad and eels to rivers such as the Severn, Wye and Usk and it could cause major impacts on the countless marine fish that feed and breed in the estuary.

"We cannot consider whether to support any proposal in the Severn until robust and peer-reviewed science has been produced to quantify the impact on fish."

Corlan Hafren has now put forward a new proposal for a low-head barrage, which supporters say would not be as harmful to the existing wildlife.

But the groups have claimed there is no strong evidence to show this would be the case.

Dr Deborah Pain, conservation director for the Wildfowl & Wetlands Trust (WWT), said: "WWT supports the search for appropriate use of tidal energy in the Severn Estuary, but it is a delicately balanced environment where ill-thought through schemes could be damaging to wildlife, homes and businesses if we get it wrong.

"We are concerned that this proposal still isn't right, and have certainly not yet seen enough evidence to suggest otherwise."

Paul Knight, chief executive of the Salmon & Trout Association, even urged the consortium to hold off until the adequate and harm-free green technology was created.

He said: "Rather than threaten the collective marine and freshwater ecosystem by building a total barrier across the estuary, surely it is more environmentally responsible and makes better business sense to wait for new technology that can harness tidal energy without severely impacting the aquatic environment and all its dependent species."