[Avodah] Avodah Digest, Vol 25, Issue 148

[Meir Shinnar]

WRT mixed swimming
This discussion has come up in the past, and, as I previously
documented, it was common practice for rabbanim and rebbitzens to go
mixed swimming at least through the 1950s -  including names that are
well known - and the standards of tzniut were comparable to what is
seen at most family friendly beaches and pools.  It has become
unacceptable - but that doesn't necessarily mean that it is assur (one
can argue about making a new issur shehachadash assur min hatorah....
:-)
but there is little basis for forbidding, for example, mixed swimming,
and allowing walking on the boardwalk next to the beach....
Meir Shinnar