Environmental groups reacted with alarm today to news that the Government was backing a multi-million pound feasibility study on the construction of a Severn barrage to generate up to 5 per cent of the UK’s electricity.

Campaigners said that a dam across the Severn estuary could have massive environmental impacts and called on the Government to look at alternative ways of harnessing the river’s massive tidal power.

The estuary, which has one of the largest tidal ranges in the world, provides mudflats, saltmarshes, rocky islands and food for some 65,000 birds in winter. In August the Government sought to designate the estuary a Special Area of Conservation, but did not rule out proposals for a tidal barrage across the Severn.

John Hutton, the Business and Enterprise Secretary, announced the feasibility study - which could result in one of the world’s biggest civil engineering projects - in a speech to Labour’s annual conference in Bournemouth today.

He described the project as "truly visionary" and added: “The Government Gordon Brown leads will not be among those who say they want to tackle global warming by moving to low carbon energy sources but then oppose every opportunity to do so.”

But the Wildfowl and Wetlands Trust (WWT), whose Slimbridge Wetland Centre is on the banks of the River Severn, said the Government must give full consideration to the wildlife in the estuary.

Its chief executive, Martin Spray, said: “WWT fully backs a shift toward low-carbon energy sources and recognises the potential benefits of harnessing the power of the massive movement of water in and out of the Severn Estuary each day.

“However the construction of a huge dam across the estuary could have a massive environmental impact on this delicate ecosystem and the wildlife that depends on it. There are alternative methods of harnessing that tidal power and WWT is calling for fair and balanced assessment of all the options and implications for the estuary’s international conservation importance so the best deal can be struck for people and wildlife.”

The RSPB said that thousands of birds and fish would be put at risk and a number of sites protected by UK, international and European law would be damaged by a tidal barrage.

Dr Mark Avery, the RSPB conservation director, said: “The Severn Estuary is one of the UK’s most important sites for water birds. A barrage would do enormous damage and its layers of legal protection are there for good reason.

“There could be much better ways of harnessing the Severn’s power and the feasibility study should examine tidal lagoon and tidal stream schemes which could cost less, do less damage and generate more energy.

“Renewable energy is hugely important and the Government should be choosing options that provide long term benefit and, just as importantly, safeguard the natural environment.”

Neil Crumpton, energy campaigner with Friends of the Earth, said that the environmental group favoured a series of “tidal lagoons” which could harness the estuary’s energy without damaging the environment.

The lagoons, around a mile offshore, would generate electricity from tidal water flowing through turbines as the tide went in and out. Mr Crumpton criticised the Government for announcing the study into the Severn barrage before the green energy watchdog, the Sustainable Development Commission, published its report on tidal power options.

“It’s unhelpful to a proper debate about the subject,” he said. “We think that tidal lagoons would be a much better option environmentally, economically, in terms of generation costs and shipping access and because lagoons have great energy storage potential.

“It’s a great pity the Labour Government seems to be closing down what should be healthy and open debate about tidal technologies, particularly lagoons as distinct from the Severn barrage.”

He also said the lagoons could be combined with a smaller barrage, the Shoots barrage, situated just below the second Severn Crossing, which could provide rail links to Wales, rather than the road proposals suggested as part of the barrage scheme.

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