An inquiry into harnessing tidal power in the Severn Estuary has rejected plans for a multi-billion pound barrage between Weston-super-Mare and Cardiff.
The investigation was carried out over 12 months by Liberal Democrat MPs, Welsh Assembly Members and councillors in the West of England and Wales.
The inquiry said it feared the large barrage would damage the estuary.
It recommended instead that a smaller barrage is built near the Second Severn Crossing.
The inquiry also urged investment in technology to help store tidal power.
The commission's inquiry said a larger Severn barrage would "do serious damage to the estuary by wiping out around 80% of the 'inter-tidal habitat'."
It also claims the larger barrage option is less cost-effective than the shorter barrage and "would cause serious economic damage to the port of Bristol".
The inquiry held evidence sessions at Cardiff, Bristol and Portishead and has studied the documents which have been prepared by the government as part of its own appraisal of options for Severn Tidal power.
The commission was jointly chaired by Northavon MP Steve Webb and Mike German AM.
"We believe that a smaller barrage offers the best mix of power output with reduced environmental impact and also offers the chance for a major upgrade to public transport through Wales and the West of England," said Steve Webb.
Morgan Parry, Head of WWF Cymru said: "We welcome the rejection of the Cardiff -Weston barrage which would undoubtedly cause significant environmental damage to the internationally-important Severn Estuary."