Plans for an alternative tidal energy project to a £15bn Severn barrage have been put forward by opponents.
Those behind the idea say it will allow shipping to move freely and keep ports at Cardiff and Bristol open and provide a balance with wildlife concerns.
Severn Tidal Fence group (STF) includes engineering groups Amec and BMT and Edinburgh University.
Conservation campaigners WWF said alternatives to the barrage should be given "serious consideration".
Backers of the barrage - which is facing a government feasibility study - say it will provide a huge amount of renewable energy at a stroke, providing 5% of the UK's needs.
A feasibility study on behalf of the Welsh Assembly Government and UK Government was announced in January.
But conservation groups claim the £15bn dam, spanning the Severn estuary from Lavernock Point near Cardiff, to Brean Down, near Weston-super-Mare, would affect wildlife.
Now STF Group has been formed and will lobby Parsons Brinkerhoff, the company behind the feasibility study into tidal power.
Key to its strategy is that a tidal "fence" would leave open major ports which it claims might otherwise be forced to close if a barrage is built across the Severn.
The fence, which it is estimated would cost around £3.5bn, is a continuous line of underwater tidal current turbines, which would force water flow through them.
It would be around 9km long, in three 3km sections, passing near to the Bristol channel's two islands.
STF GROUP PARTNERS
Amec Engineering group
Marubeni Europe plc Trading and investment house
Edinburgh University Researcher into tidal currents and tidal stream power
Econnect Renewable energy projects company
BMT Engineering, science and technology consultancy
IT Power Sustainable energy consultancy
NaREC New energy research and development
Pulse Tidal Tidal stream generating development
Source: STF Group
Although the fence would produce less energy, STF Group claims this approach would be a compromise between conservation, commercial interests and renewable targets.
Marc Paish from the STF Group said the fence would have a capacity of 1.3GW - slightly more than Sizewell B nuclear power station - and provide around 1% of the country's electricity supply.
"Importantly, the fence would allow shipping to pass through and so keep the ports of Cardiff and Bristol open, whereas the barrage risks their closure," he said.
"The fence also allows the migration of salmon, and it would only slightly reduce the areas of mudflats which are an important habitat for migrating birds.
"It would also reduce high tide levels upstream enough to significantly reduce the risk of flooding."
In addition to the tidal fence, the group is suggesting a small barrage or tidal lagoons to ensure continuous output - and which could bring the total capacity to 2% of UK supply.
The fence would produce most power at the middle of the tidal cycle, whereas the barrage or lagoon would produce most power at high and low tide.
STF estimate the project could create between 8,000 and 13,000 direct and indirect jobs.
Conservation campaign group WWF welcomed the idea and said the alternative proposals deserved "serious attention", with the barrage occupying almost entirely all the focus so far.
Morgan Parry, head of WWF in Wales said: "We have argued for many years that there are better ways of generating power from the tides than through fixed concrete barrages and we must keep all these options open."
He said there were many options and ministers were "wrong to focus exclusively on the barrage."
A Department for Business spokesperson said they made it clear what they would look at all options, including barrages, lagoons and other technologies.
"The study will assess in broad terms the costs, benefits and impact of potential schemes and how they would affect the environment and the region," said the spokesperson.
"As part of the first stage of the feasibility study we asked for tidal range proposals to be suggested. We are now considering those suggestions."