Skinnydipping in High School

Over at the education section, there's a rather long thread on the subject Boys Nude Swim Gym Class. It consists of a lot of us old enough to have experienced this--as I did, at Jefferson and East, 1962-1968--reminiscing, complaining, analyzing, and trying in general to make sense of it. We determined it was almost universal, at least for boys in high school, but only during a given period, and is now long past.
We solicited info from anyone we could find, and it occurred to me I might get that info from a post here. Specifically, I'm wondering if any guys (you girls were exempt, delicate little flowers that you were) remember this, remember what justification you were given, and remember when it ended.
I was never told why, and I left East in 1968, and Rockford in 1980.
Any input useful.
Live long and prosper.

It is my understanding, from various persons in the 50+ range, had swim classes in the nude. Most of these men are from Chicago high schools. At the former YMCA,(on water St?) the men supposedly swam nude. At that time there were no females at the "Y"

They also never gave an explanation as to 'why.' It is interesting that this was a time that modesty was paramount.