Stroud District Council cited the Equalities Act 2010 when explaining its reasons for admitting men to the weekly sessions at the Pulse leisure centre in Dursley, Gloucestershire.
The women-only classes had been held at the centre for years without complaint.
The council has now apologised, saying it "should have taken legal advice" before acting so quickly.
The decision to make the classes open to both men and women followed a single complaint that they were discriminatory, with the council saying it hoped people would "understand we have to abide by the law".
The move prompted derision on social media.
A petition to "bring back ladies only swimming" also attracted nearly 4,000 signatures and was shared by celebrities including comedian Frankie Boyle.
One of the most vocal critics was county councillor Loraine Patrick, who said she was "astonished, furious and outraged" at the decision.
Explaining the reasons for the U-turn, a district council spokesman said: "There has been a strong response to our decision to end the ladies-only swimming sessions after we received a complaint alleging that we were breaching equalities legislation."
He said that "with the benefit of hindsight" the council should have taken more time to consider its response "rather than acting so quickly".
The spokesman added: "We will be taking the next few weeks to consult with our customers directly to get their views before we decide on what to do."
Women-only swimming classes that were scrapped by a council for legal reasons have been reinstated.