Swindon Borough Council leader David Renard says the new Grade II Listed status of the Oasis will make reopening harder.
The iconic dome, slated for removal in a recent planning application to prepare the leisure centre - closed since last November - for re-opening, is protected under the terms of the Listing.
Cllr Renard said: "We have always been absolutely committed to a new, fit-for-purpose leisure facility on the site of the Oasis for local residents and visitors to enjoy, but there is no doubt the listing of the dome will make that process a lot more difficult, not to mention considerably more expensive.
“Our job now is to sit down with [owners] SevenCapital to see if there is any way it can bring forward a viable and sustainable plan for a modern facility on the Oasis site, despite the constraints that have been placed around the 1970s dome."
Last year's closure came after then-operator GLL said it could not continue to operate the facility.
The organisation said the centre was not economically viable and was losing significant amounts of money.
The council said in a social media post following the Listing announcement: "Since that time, SevenCapital, who have a long lease for the Oasis, have been working on plans to give the leisure centre a sustainable future and recently submitted a planning application to the Council for a new and improved facility to meet the needs of the community.
"Today, Historic England has confirmed that an application to list the Oasis has partially been approved by the Department for Media, Culture and Sport (DCMS). The listing has been limited to include only the swimming pool’s domed roof. The dry-sports side of the building; the waterslides, their launch tower and splash pool; the linking entrance block; and the service structures are not included in the listing."
The new status of the dome was greeted with delight by campaign group Save Oasis Swindon. Founding member Neil Robinson said: "I can't believe we've done it. I cannot believe that the Oasis has been granted Listed status.
"I created this campaign a year ago because I was devastated that they closed the Oasis down. I was using it right until it closed with my daughter, and it was a massive loss to Swindon to lose the Oasis.
"The Oasis is an iconic building in Swindon that people know from miles around. People travel from Gloucestershire, Oxfordshire, from all over the country around the south west to visit the Oasis because it's such an iconic building in Swindon.
"It always deserved to be a listed building, and for the past year there's been a really hard campaign.
"I've never done anything like this before, but I felt passionate about it and I wanted to save it for Swindon."
"Now SevenCapital haven't got an excuse. They have to get on with restoring the Oasis now for Swindon."
SevenCapital have been approached for comment.