The Royal Society for the Protection of Birds is warning that a scheme to harness the power of the River Mersey could be an environmental disaster.
Detailed plans are being drawn-up for a "Power from The Mersey" scheme, with backing from the North West Development Agency (NWDA).
Peel Energy - the firm bidding to harness the Mersey's tidal flows - aim to produce detailed proposals by 2012 and envisage the project's completion by 2020.
When the idea of harnessing the Mersey's tidal power was first mooted in the 1970s a barrage across the estuary was the only option proposed.
More recent drafts of the scheme have included other, less invasive, porposals like a series of paddle-wheel generators or underwater turbines.
But the RSPB is warning that concerns about cost-efficiency could make a barrage the most likely option, despite the fact that it would destroy rich wildlife habitats.
To support its claim the RSPB cited an new report detailing the devastating impacts of a storm surge barrier built across the Oosterschelde estuary in Holland in the 1980s.
The Society warn that the experience of the Oosterschelde barrier should serve lesson of the potential peril of a barrage on the Mersey.
The RSPB fear that Mersey scheme promoters will push for the the most cost-effective a barrage option.
The Dutch report on the Oosterschelde barrage found that:-
* Increased erosion has led to the loss of mudflats along the estuary, leading to higher waves and water levels. Huge sums will have to be spent on strengthening coastal defences to protect lives and property.
* By 2050, the tidal flats of the Oosterschelde will have more than halved, destroying feeding grounds for internationally important numbers of birds.
* Salt marshes disappeared.
* Less intertidal habitat meant less shellfish and fewer birds.
* Shipping channels became shallower and harder to navigate.
* Shellfisheries was hit because of loss of habitat for cockles and mussels.
* Tourism was be hit by the loss of wildlife interest.
RSPB Conservation Manager for Northern England, Peter Robertson said: "This report makes grim reading.
"It's the closest we can get to proof that the creation of a barrage across an estuary would cause devastation.
"The Oosterschelde is very similar to estuaries in the North West in many ways and it is being damaged beyond repair. We must ensure that the same fate does not befall the estuaries of the North West.
"The Dutch built their barrier to prevent deadly storms from claiming lives. Ironically, it has now led to an increased risk of flooding behind the barrier, but it could be argued they had little choice at the time.
"In the North West, we do have a choice. Barrages would not be built to stop storm surges but to harness the tides and generate electricity. There are other, far less environmentally damaging ways to do that. We only have one opportunity to get this right on each estuary so we need to explore all potential solutions.
"We have long said the Government should invest in innovative schemes, which offer the potential to put the UK and UK engineering at the forefront of tidal power without the risk of floods, loss of wildlife and livelihoods."
A spokesman for the NWDA said: "At the moment the plans are still in their infancy and we continue to look for the most cost-effective and environmentally sound option."
But Peter Robertson, added: "We've been working very closely with the NWDA to examine possible options for gathering renewable energy from the River Mersey.
"Naturally we are fully supportive of environmentally-friendly energy sources, but we must also remain mindful of the potentially devastating environmental consequences of any new technology.
"The NWDA have proposed four possibilities, of which a tidal barrage across the Mersey estuary is the simplest and most energy efficient way, and probably the cheapest.
"We are concerned that there have been similar examples of using tidal barrages where the environmental impact has been catastrophic.
"The Oosterschelde is an estuary very similar to the Mersey and it has lost nearly all the natural wildlife.
"There has been a massive impact on fishing in the river, and a change in the rivered which has damaged shipping channels.
"In fact, the tidal barrage has even caused flooding, because such a large barrier significantly changes the flow of water.
"We need to consider a less invasive compromise, even if it does cost a little more money.
"The potential to cause damage by taking a punt at the cheapest option would be absolutely disastrous."
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