I swim regularly for exercise because I have RA.  It is great for flexibility and cardio.  If I didn't it's likely I'd be on disability instead of working. In winter I swim indoors during the senior citizen's hour.  (Nobody is there to gaze at bodies.  The activities are for physical therapy.)  In the warmer months, I swim at the ocean beach on week days after the lifeguards and crowds are gone. Usually, the only ones present are elderly Russians and Ukrainians who sea bathe year round for health purposes.  I also swim at my cousin's farm pond while on vacation.  At least a few times each summer, I swim off my brother-in-law's boat anchored off of Cape Cod.  I'm well past the age where I'm either tempted or am tempting to others, nonetheless, I avoid the typical beach goers.  Theres nothing tempting to me about nearly naked people full of tattoos and piercings!  Yuck!  I have two swim dresses I sewed for myself that are modest, even when wet, and far less expensive than any of the commercial models.  

Yes, let's get into some Catholic doctrine.

Has anyone brought up the phrase yet, "Unnecessary occasion of sin"?

A beach is an unnecessary occasion of sin. A grocery shop is a NECESSARY occasion of sin. We have to eat in order to live. We do not need to sunbathe or swim in order to live.

See the difference?

The actual danger, or occasion of sin, could be the same. Heck, it could be WORSE at the grocery store in certain circuмstances (30 young, attractive women in shorts and immodest clothes at the grocery store vs. only 5 near-naked women a good distance away at the beach on a given Monday late morning) but it doesn't change one's clear, rational, Catholic judgment on the matter.

It's all a question of: is it necessary or not to be there?

Thank you!