Nude practice every morning - no suits allowed. Even when I was an 18 year old senior, nude was the rule.
Nude swimming was generally "justified" on the basis of fibers clogging up the pool filters. Of course, if the girls got to wear suits, how did this make sense having the boys nude?
Just to confirm, swimming naked was not because the filters couldn't handle the lint. The majority of clogging mass in filters is hair - a vast majority. And it is more likely to be head and body hair from men than head hair from women. So, if anything, they were adding more hair to the mix by swimming naked.
Swimming was a summer term activity. We only got to wear trunks when competing with other schools.
"As a coach my swimmers never wore suits, either in practce or competition, those guys were athletes who enjoyed showing off their well toned bodies."
“My generation we had to swim nude at the YMCA, at jr. college etc. and it was accepted as norm even when there were female supervisors. It was assumed by females that males did not have modesty issues and guys began to say- heck we don't! The presumption by moms and other females that males should be xposed to females but not vice verse.”
Evidently, in the 50's, 60's, and 70's, boys in America were forced to swim nude in swim class, on swim teams, and at the YMCA. This was to "prevent bathing suits from clogging the drain", though girls got to wear bathing suits. Also, it prevented boys from having to be responsible for soggy suits, though girls were readily entrusted with such a arduous task.
Perhaps there were women on the school boards, or dominating their husbands on the school boards, who, like you, thought it would be funny to make the boys strip naked for swim class. It makes more sense than the pool filters business.