The campaigners met this week to build opposition to Wrexham Council's plan to axe Plas Madoc, which is used by people from Lllangollen, along with the Waterworld leisure centre in Wrexham as part of a cost-saving exercise.
They point out that the proposed savings from closing the two centres and building a smaller pool complex next door to the existing Waterworld site would only save £97,000 a year, according to a report by consultants.
Alison Roberts, for the campaign, said: "The savings of £886,000 do not account for any demolition or site clearance costs, which are likely to be substantial. I think we need to question the reliability of the repairs and maintenance costs.
"The huge and disproportionate figure given for Plas Madoc was derived from a conditional survey, based on a visual assessment. We question this and request an independent in-depth assessment to ascertain true and reliable figures.
"These are well-used leisure facilities that our communities want to maintain. It's vital that the council takes that on board before making any decision."
The council's executive board will vote on January 14 on whether to go ahead with the closure proposal and the campaign is planning to unite local communities in a mass protest on the Saturday before outside Plas Madoc.
Fellow campaigner Darrell Wright said: "We're organising a peaceful but noisy protest for all the community outside Plas Madoc at mid-day on Saturday, January 11 to show how much our leisure centre means to us.
"This is where local children learn to swim and play, where adults can use a gym and other sports facilities and where people can get rehab in the community. Lots of various sports groups meet there and will be left homeless if the council presses ahead with these short-sighted plans .
"We want people to turn up with pots and pans to make some noise as well as wearing their sports gear.
"This has all happened so suddenly just before Christmas and many people we've spoken to while collecting signatures on our petitions were unaware of the threat to close. So we've got to act quickly and make sure everyone puts pressure on the 10 councillors on the executive board to consider the impact on the community before the close these sporting facilities.
"We hope the thousands who are on our Facebook page, the thousands who&n bsp;have already signed our petitions and everyone who is against this foolish plan will turn out on the 11th to show their support. We will also be lobbying the meeting in the Guildhall on Tuesday, January 14."
* The cost of closing both Waterworld and Plas Madoc is £886,000; the cost of building a smaller Waterworld is £789,000 per year. The figures are taken from the consultants' report - http://www.wrexham.gov.uk/MinutesData/HomesEnvCom/Reports/haed5913s.pdf (page 22 of the consultant's report at the end of the committee report).