A mysterious happening at a women's-only swimming meeting sparked a global social media obsession, with thousands of people from around the world weighing in with theories about what transpired.

The 'serious incident' on Sunday night, at Sunshine Leisure Centre in Melbourne's west, forced the regular event to be cancelled, with management only cryptically citing 'poor behaviour' without explaining further what had unfolded.

This only fuelled the global online frenzy and led to feverish speculation the drama involved anti-trans protesters, men attempting to gatecrash, or a political dispute.

The sessions are held after hours, and there are only three female staff members allowed to work to maximise privacy for the attendees.

Daily Mail can now reveal that it was actually a physical fight between female swimmers that sparked the ban, understood to have erupted in the changerooms after the session had ended, over the use of showers.

With apparently no security at the event, Brimbank City Council has since cancelled the sessions while it reviews how they can be better managed outside normal business hours.

A Victoria Police spokeswoman confirmed officers were called to reports of a fight at the centre on Sunday night just after 7pm.

'No one was injured. A formal report has not been made to police by any of the parties in relation to the incident,' the spokeswoman said.

The centre announced the suspension in a cryptic Facebook post on Wednesday. 

'Please be aware that following a serious incident involving poor behaviour at our last session, we are temporarily suspending our Sunday night Women's Only Swimming Sessions until further notice,' the post read.

'This pause is to investigate the incident, review the offering, and determine its viability moving forward. We apologise for the inconvenience and appreciate your understanding.'

With officials initially refusing to reveal what had happened, bizarre theories ranged from someone befouling the pool, to swimmers skinny-dipping, to a transgender access dispute, and, in one particularly colourful claim, university students releasing a hippo into the pool that supposedly required a crane to remove.

Scores of people checked in from London pubs, Scottish living rooms, Canadian lunch breaks, Greek couches, Tunisian holidays and Californian offices, flooding the comments section with speculation while wondering why Facebook had served them the post in the first place.

One London pub-goer wrote: 'I am sat in a pub in London, why this is on my feed I'll never know... however, what happened?'

Another added: 'I'm on holiday in Tunisia and need to know.' 

As speculation ran rife, Brimbank Mayor Virginia Tachos issued a further statement later that day to address 'incorrect information' circulating about why the after-hours sessions had been temporarily paused. 

'To be clear, this pause is not due to a protest against the Women's Only Swim Session by men, nor is it because of a transgender woman allegedly being refused entry. These claims are entirely false,' she said in a statement.

'The sessions have been paused following a serious safety incident that occurred on Sunday September 13, where participants and Brimbank Leisure Centre staff were exposed to unruly behaviour that occurred amongst a number of attending patrons.

'Brimbank City Council does not tolerate violence or unsafe behaviour. The health and safety of our patrons, our staff and the broader community is our absolute priority.'

Cr Tachos said the council was conducting a full investigation and a comprehensive risk and safety assessment to determine whether the program, staffed by three females, could be delivered safely in the future.

'We know these sessions are important to many women in our community, providing an opportunity to exercise and connect with others in a welcoming, safe and comfortable environment,' she said.

'Council has an obligation to ensure they are delivered in a way that is safe for everyone – including the Brimbank Leisure Centre employees who support and deliver the program.'

Cr Tachos said council would provide a further update once the investigation and safety assessment have been completed.