Let’s end this foolishness once and for all.
Mixed swimming/bathing may be assur, but it is not an issur (I call on Wolf here to help explain the difference as with Tamei/Tumah).
Let’s set aside for the moment the issue of tsnius and shmiras einayyim. There is still another issur that prohibits mixed swimming. It is kiruv l’arayyos – the same issur that prohibits sharing a bed. Armed with that knowledge, one can start to understand the distinctions:
- A father and daughter may share a bed until a certain age/time that is explicitly stated in Halacha.
- Two men may share a bed since it is explicitly stated in Halacha that they are not nechshad l’arayyos.
- A blind man is no different from a pikayach when it comes to sharing a bed because the issur has nothing to do with sight.
The same applies for swimming.