She said she chose to use the men’s changing room with her two-year-old son because it was less crowded than the women’s.
Writing on Mumsnet, she said: “There is a dad there getting his daughters dressed (fine). He's in the pool and he's down to his underwear.
“Anyway, dad of daughters decides to get dressed. He drops his pant and is stark naked in front of his daughters.
“He is also by the door so if another parent was coming in their child would have walked into his penis!
"There are cubicles. He could have used a towel as well."
The Mum asked if she was being unreasonable to find the man’s behaviour bizarre.
“His bum was also hairy and unattractive,” she wrote.
Comments flooded in from other parents, but forum users were divided over whether the man was in the wrong.
One wrote: “I don’t think it’s weird if he’s in the men’s changing room.”
Another said: “So you were upset because you saw a man’s penis in a male changing room? Are you female? If so you shouldn’t have been in there.”
Some commenters argued the dad should’ve taken more effort to keep himself covered – especially in the presence of other children.
"Not prudish and I know we've all got a body. But this was totally unnecessary. It could have been other little girls besides his daughter," one person wrote.