I don't have a problem with this, many women are put off from swimming in public because they have body issues especially where men are present.
Rather than boycott the event I would urge any woman to attend, regardless of the colour of their skin or their religious beliefs.
My sister has not swam in public since having a double mastectomy even though there are some lovely costumes she could wear. I have told her about this event and she is planning to go with friends, so she can test a costume out in use.
The leisure club I used to be a member of had regular nude sessions, male only, female only and mixed. If you weren't prepared to swim naked you couldn't use the pool or go in the pool area. Also there were parent and baby only sessions, lane swim sessions for serious swimmers, splash sessions for families and lifeguard training sessions. The timetable was clear and nobody complained.