Surprisingly often, I deal with the issue of raccoons causing problems in swimming pools. Raccoons love water, and they're drawn to rivers and lakes. In actuality, the raccoon's latin name, Procyon lotor means "washes with palms" - those creatures were so named because they sometimes wash their hands, and even their food, in water. Cute! But where raccoons eat and live, they poop. And like a lot of animals, they prefer to hide their stool (like a cat pooping in the sand), and thus they like to poop in water. If you have a swimming pool, raccoons will likely use your pool as a toilet. This is all the more common if you've got some shallow steps leading down into the pool.
So how do you resolve a problem with raccoons in your swimming pool? The best approach is often to trap and remove and relocate the animal, so that it no longer has access to a pool at its home range. Raccoons are extremely crafty and resourceful, and they are also very brazen with individuals, so tactics that attempt to deter them or scare them off do not usually work.
If you do trap the offending raccoon, please be kind. Raccoons are very intelligent and even psychological animals (it's true!) So it would be wonderful to drive the animal to an area far away, at least ten miles, and release it.