The iconic domed roof of Swindon's Oasis Leisure Centre will be removed if a planning application is successful.
The campaign responded: "Seven Capital have submitted some new very concerning plans to the council today - to demolish most of the Oasis and rebuild with a design that destroys our iconic landmark. We are urgently seeking more information.
"No listing decision has yet been made yet. So they are either trying to stop the listing, or already know the building won't be listed. We don't know yet."
The application lists several planned changes at the Oasis, which was built in 1976 and soon became a major draw, attracting people not just from the Swindon area but from much of of the surrounding region.
The document mentions: "Replacement of dome roof and other works to the eastern 'wet side'; demolition of the western 'dry side' and replacement with new entrance reception, changing facilities, gym and associated facilities; MUGAs, revised car parking and landscaping."
The Save Oasis Swindon Campaign has announced that it is working with architectural heritage organisation the Twentieth Century Society, which will make an announcement next week.
The campaign and Swindon Borough Council have been approached for comment.
The leisure centre was built in 1976 and, thanks mainly to its wave machine and other innovations, rapidly became a major regional draw. It is famously a footnote in the history of British music thanks to Noel Gallagher, who chose its name for his band after visiting while working as an Inspiral Carpets roadie.
Last November GLL, the organisation then operating the centre on behalf of owners Seven Capital, announced that it would close. GLL blamed the impact of the pandemic.
SevenCapital Managing Director Angus Michie said: “We understand fully how important the Oasis is to the people of Swindon and we have explored every possible solution we could to feasibly allow the facility to be reopened so it provides a similar, but significantly enhanced experience.
“To be able to do this and give the Swindon community what they deserve from this kind of facility, which includes ensuring it is safe, energy efficient and affordable, sadly this means the dome roof needs to be replaced.
“All the measures we are proposing would effectively lead to better functionality and lower running costs of the Oasis, which in turn will make it more sustainable long-term and importantly, cheaper for users.
“I am confident that the solution we are putting forward for the Oasis will give it the longevity to be enjoyed over the next 50 years and beyond as the iconic centre it has been since the 1970s.”
Borough council leader David Renard said: “The Oasis holds a special place in the hearts of people in Swindon and beyond and we have always been clear that we wanted to see it reopened so it can be enjoyed by families for many more decades to come.
“I am therefore extremely pleased that SevenCapital has shown its commitment to investing in an enhanced, modern leisure centre which we hope will be the envy of many towns and cities in the region, just like the Oasis was in its heyday.
“The current building has a number of issues and is hugely energy inefficient and with the Council committing itself to a carbon neutral target by 2030, we need to ensure the Oasis has both a green and sustainable future.
“This is an important first step, but there is a long way to go both with the application, which will now be subject to the normal planning process, and our ongoing commercial discussions with SevenCapital on this exciting proposal.”