I've been swimming, ( or looking like a swimmer lol i'm not a great swimmer to be honest) As a female, I actually just bought this high waisted two piece from american apparel for a trip. We can wear two pieces dependent on the location, i never felt comfortable just baring it all even before my stoma, so i always wore a sarong. Thats what i'll do if i get the courage to wear the two piece.
For men i've seen men just pull their shorts up, not urkle like drawstring helps.
I've read that you can't do deep sea diving because the bag will enlarge, but i've also read you can do like the shallow scuba diving that they do on vacations. I haven't had the courage to try yet