Diarrhea
One of the top causes of post-swim illness is a parasite called cryptosporidium (crypto for short), which leads to diarrhea, stomach pain and nausea. According to the new CDC report, of the 69 outbreaks associated with treated water, more than half were caused by crypto. Symptoms can last for up to two weeks. The parasite ends up in the water if feces (even trace amounts from someone who didn’t shower first) of an infected person gets in the pool. The bug is resistant to chlorine and survives outside the body for long periods.