I have literally never been to a publicly accessed pool that didn’t have this sign, and that’s including traveling all over the country so it’s not like I just live in a niggery area (though I unfortunately kinda do). I think most of the people commenting here just aren’t very observant; your anus isn’t as waterproof as you think it is, and getting in the pool allows whatever bacteria is causing your diarrhea to transfer into the water and into other people’s anuses. Or eyes or mouth or whatever else might get water in it.