Are you serious? Where was this?
(Maybe I should ask, when was this? 14th century? Ancient Greece? Weirdest thing I've heard all day...!)
I am serious, this was here in Victoria in the 50's and 60's as well around North America.
The following is a quote from Wikipedia
...Before the YMCA began to admit females in the early 1960s, swimming trunks were not even allowed in the pools,[6] and high school swimming classes for boys sometimes had similar policies, citing the impracticality of providing and maintaining sanitary swimming gear and clogging swimming pools' filtration systems with lint fibers from the swimsuits. These practices were common because of the perception that there was nothing wrong or sexual about seeing members of the same gender in the nude, especially in these indoor contexts among equals in 'birthday suit uniform'...
You can Google Images "YMCA nude boys swimming" and see for yourself.