You can not get pregnant by swimming in a pool where a man has recently ejaculated.
It doesn’t matter how big (or small) the pool is.
It doesn’t matter if you’re naked.
It doesn’t matter if he ejaculates while swimming right next to you holding you in a fond embrace.
The only way you can get pregnant from swimming in a pool where a man has recently ejaculated is if said recent ejaculation happened while he was having vaginal intercourse with you in that pool… and if that’s the case I recommend you pick up a life preserver along with a package of condoms. You’re not just risking pregnancy… you could drown!
Explanation for why you can not get pregnant by swimming in sperm infested waters:
The vagina is a potential space, not an open cavity waiting to engulf any passing sperm and suck it up through the cervix to where it can fertilize an egg. There is no way for the sperm in the pool to get inside you unless it is hand delivered by a penis. Penis delivered by a penis? Unless is delivered, during intercourse, by the penis express.