Environment Agency chief executive Barbara Young this week slammed the proposed Severn Barrage scheme for its negative environmental impact on the estuary's unique wildlife.
"A project to deliver 5% of the UK's energy at the price of wrecking valuable wildlife is not the way forward," said Young.
"If you wrote someone a note, you would not reach for the Mona Lisa to write it on," she said to applause from delegates at the Environment Agency's "Adapting To Change" conference, this week.
"But that is what you would be doing with this scheme."
Also speaking at the conference was Energy minister Malcolm Wicks. "The [barrage] proposal is being taken seriously," said Wicks.
"The environmental impact of the project will [also] be taken seriously. But we need grand projects on that scale."
He said such projects were essential if the UK is to meet the European Union target of having 20% of its energy from renewable sources by 2020.
Wicks also hinted that the UK may not need to meet the 20% threshold, and was lobbying to have the 20% as an EU average, not an absolute target for every EU member state.
Sir Robert McAlpine corporate development manager Roger Hull, who is spokesman for the Severn Tidal Power Group (STPG) said: "There are environmental advantages to the scheme, which will save around 500,000 tonnes of CO2 per month."
The group is a consortium of Alstom, Balfour Beatty, Sir Robert McAlpine and Taylor Woodrow.
He added that the last environmental assessment for the project was 20 years out of date. It was included in a report on Severn tidal power which was published in 1989.
"The Royal Society for the Protection of Birds concluded in 2005 that because the temperature in the area had already increased by 1.5° C, wading birds had already migrated to the Wash," said Hull.
The government has promised a new Seven Estuary tidal power feasibility study. This will include an assessment of a barrage's environmental impact on the region.
Consultant Parsons Brinckerhoff (PB) is promoting a rival smaller scheme to the STPG proposal sited just south of the Severn Bridge.
PB environment and planning director Peter Kydd said its Shoots barrage would produce one-sixth of the energy, but at one-eighth of the cost, and with reduced environmental costs.
According to Friends of the Earth environmental campaigner Neil Crumpton, the Shoots scheme would be the "lesser of two evils."
Crumpton said that the Shoots scheme could combine electricity generation with a new rail alignment over the Severn to replace the ageing Severn tunnel.
"But it is not a clear case," he said. "The environmental lobby is calling for an all technologies study to be studied. "
Severn: The Facts
- The Severn Estuary has the second largest tidal rage in the world, making it ideal for a hydroelectric scheme. It could generate 5% of the UK's energy needs.
- The Severn barrage would generate 8.64GW, and cost Ł14bn, running across the Severn Estuary from Cardiff to Weston-Super-Mare. It would impound around 70% of the estuary.
- The Shoots barrage would run just south of the Severn Bridge, generate 1.05GW and cost around Ł1.6bn. It would impound only around 23% of the estuary. Its lesser power could be supplemented by tidal lagoons which would not have a significant environmental impact.