A Proposal to build a Barrage across the Severn Estuary 'could be absolutely devastating', MPs have heard. The Angling Trust, Wildfowl & Wetlands Trust (WWT) and RSPB told the House of Commons Energy & Climate Committee they all supported tidal energy development in the Severn, but that the current proposal lacks detail and claims that it would not unacceptably damage wildlife and large areas of habitat are "not realistic".

River Severn estuary – Nicholas Mutton 

As well as doubting claims about the environmental impact of the barrage, all four organisations expressed support for future alternative smaller projects in the Severn Estuary to test and develop new tidal energy technology which Britain could export globally.

Angling Trust National Campaigns Coordinator 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: "Claims that these turbines are fish friendly are absolute guff. This is 24/7 fish mincing. Turbines kill fish above a tip speed of 6-7 metres per second. The Hafren proposal is for a tip speed of 9 metres per second. How on earth can they make press statements that these are "fish-friendly". They are simply not. "This drives a coach and horses through all environmental protections that governments have signed up to. The impact could be absolutely devastating on both the commercial fishery, on the recreational fishery and on highly protected habitat."

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."

RSPB Head of Site Conservation Policy Kate Jennings said experiences elsewhere suggest smaller projects would be a better way to test new technologies rather than repeat experiences in the Netherlands: "The experience in the Eastern Scheldt estuary in the Netherlands where they built a storm surge barrier in the 1980s is the best comparator for the Severn Barrage. What they found is that 30 years after construction the estuary is still losing intertidal habitat. They think it will go on losing habitat for at least a century. "The official Government study into the Severn Barrage proposal in 2010 showed that 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."

Kate also addressed claims that a barrage would reduce flood risk by protecting against storm surges, telling MPs a barrage could actually increase flood risk upstream: "There are other forms of flood risk. A significant one being fluvial (rivers) and managing that relies on the ability to get water out of the Severn. Holding it back behind a barrage would compromise that and tide-lock drainage. We don't have enough details of the proposals."

The Angling Trust, WWT, and RSPB have also agreed a joint position regarding the Severn Barrage with several other environmental organisations – WWF-UK, the Wildlife Trusts, Wye & Usk Foundation, Marine Conservation Society, Severn Rivers Trust, Salmon & Trout Association and Campaign to Protect Rural England.

The agreed position was sent in a letter to Hafren Power and Peter Hain who supports the barrage proposal. The position was summarised as: "We support the deployment of renewable energy as an essential element of the steps required to decarbonise the UK economy, and acknowledge the potential of the Severn Estuary for renewable energy generation. "However, we believe that renewable energy deployment can and should be delivered without unacceptable impacts on the environment. To date we have not been presented with sufficient detail on the current proposal, or any assessment of the impacts of that proposal, which would allow us to consider the extent to which its impacts would differ from those of the completely unacceptable high head Cardiff to Weston barrage (especially in the long term). That said, we remain deeply sceptical that a shore-to-shore barrage can be delivered without unacceptable impacts on the environment. "Given the likely scale of the impacts of such a development, and the associated environmental, social, technical, legal and investor challenges and risks, we believe that an approach which focuses on smaller scale deployment, sited and designed to maximise energy output whilst minimising environmental impact, is more likely to deliver an acceptable solution in a timescale compatible with the urgent need to address climate change and maintain electricity supply."

Read the full statement on the Angling Trust website