Ewww.
“When we go swimming and we complain that our eyes are red, it’s because swimmers have peed in the water,” says Michele Hlavsa, chief of the CDC’s healthy swimming program. “The nitrogen in the urine combines with the chlorine and it forms what’s known as chloramine and it’s actually chloramine that causes the red eyes. It’s not the chlorine itself. It’s chlorine mixed with poop and sweat and a lot of other things we bring into the water with us.”
Source: What makes your eyes red in the pool? It’s not the chlorine – TODAY.com