A BILLION-POUND barrage across the Severn Estuary could be approved this year, despite further criticism on the impact it could have in Gloucestershire.
Proposals for the barrage from Hafren Power have been questioned by several organisations, including the Wildfowl & Wetlands Trust (WWT), which runs the wetland centre at Slimbridge.
The WWT, RSPB and Angling Trust told the House of Commons Energy & Climate Committee they all supported tidal energy development in the Severn, but described claims it would not unacceptably damage wildlife were "not realistic".
All three back alternative smaller projects in the Severn Estuary to test and develop new tidal energy technology, which Britain could export globally.
Former minister Peter Hain said the barrage had been re-thought so that fish and birds would not be threatened.
The barrage, which could provide as much electricity as 3,000 wind turbines, could be built by 2024.
It could provide five per cent of the UK's electricity needs, and the cheapest energy on the market, for more than 120 years.
Investors in the £25 billion project are not asking for any public money, b but issues over wildlife have been raised.
WWT chief executive Martin Spray told MPs: "This represents such a massive investment and such a massive change to the estuary that we do need more information.
"We have got to get a little more clever about how we address the environment.
"There is potential for energy generation, but we have to come up with environmentally sustainable, acceptable and sensible solutions."
Angling Trust National Campaigns co-ordinator Martin Salter told the committee a full-width barrage across the estuary would mean fish dying due to sudden changes in water pressure and salinity and through turbine strikes.
He said: "The impact could be absolutely devastating on both the commercial fishery, on the recreational fishery and on highly protected habitat."
Kate Jennings, head of Site Conservation Policy at the RSPB, said birds and other wildlife sites could suffer.
She said: "The official Government study into the Severn Barrage proposal in 2010 showed there would be significant effects on the populations of 30 species of birds and that, in addition to the Severn, it would also have negative impact on at least five other internationally important wildlife sites nearby."
WWT, RSPB and the Angling Trust have agreed a joint position with other environmental organisations, including Severn Rivers Trust, Salmon & Trout Association and Campaign to Protect Rural England.
The agreed position was sent in a letter to Hafren Power and Mr Hain, who is backing the barrage, stating smaller-scale projects, designed to maximise energy output while minimising environmental impact were a better option.
Plans for the barrage were previously rejected by the Government two years ago.