CALGARY -- An escalating debate over a nudist swim at a public swimming pool has prompted the City of Calgary to cancel the event over concerns about security.

"We've had a review completed by Calgary Police Service and corporate security that has led to these arising concerns," James McLaughlin, acting director of Calgary Recreation, said Thursday.

"Safety concerns are related to the volatile public commentary regarding this public booking and they cause concerns for all users of the facility."

The Calgary Nude Recreation club had sold tickets for a swim night on Sunday at the Southland Leisure Centre. The club described the private, after-hours event on its Facebook page as a way of snubbing winter.

Word of the event prompted an online petition urging the club to cancel the swim or ban children from attending. The leisure centre's Facebook page was inundated with negative comments about the event including some that threatened to bring "cameras and baseball bats."

Calgary police say they received a report of a threat Monday to the leisure centre due to the swim event. Although they say officers determined there was no immediate danger, the incident is still under investigation.

Event organizers posted reaction to the city's decision on the Calgary Nude Recreation club Facebook page. They called the move a "terrible precedent."

"It is outrageous that lawful recreation can be prohibited by an incredibly vocal minority. These people must NOT be allowed to dictate public policy with threats against law-abiding citizens engaged in lawful activities," reads the post.

"Calgary Nude Recreation recognizes that the City of Calgary is not the bad guy here. We will continue working with the city to reschedule a future event."

The group also said its new goal is to establish a legal clothing-optional stretch of river within reasonable distance of the city core. It warned that cancelling the event at the pool won't make nude activity go away.

McLaughlin said city facilities have held nude swims for years. The cancellation was not due to the nature of the activity, but solely because of security, he said.

"It actually speaks to the concern the administration has for the safety and security of all our users."

By Thursday afternoon, an online petition opposing the event had racked up 20,000 signatures.

"Respect the concept and believe in an 18+ setting it could be a popular event. However, having naked children around a bunch of naked adults doesn't seem like a good idea for any reason," said the petition posted by April Parker.

"Sexual predators will be on the prowl -- having an event like that is just like Christmas to them."

Calgary Coun. Jeromy Farkas, whose ward includes the city-operated leisure centre, said his office was contacted by a lot of people concerned about the swim. He suggested there may have been a solution to the debate.

"Given that I'm very live and let live ... I am disappointed that we couldn't proceed with this in an 18-plus manner."