Do you girls pee in swimming pools or what do you usually do when you got to go?

> some pools have a dye that turns urine blue ...

That dye does not exist. It's a story parents tell children to scare them out of peeing in the pool. Also, unless you have an infection (such as a bladder infection), urine is STERILE. So peeing in the pool is not unsanitary.

Seriously, if I were you, I would just pee in my bikini, whether it's in the pool or in the ocean. I'm not a girl, but that's what I do.

Of course, you could always remove the entire bathing suit, or pull the crotch to one side, and pee in the toilet.

Do whichever you're more comfortable with doing.