E. coli, Giardia, Campylobacter... Oh my! There are a lot of nasty parasites and bacteria that can be found in swimming pools, even the dreaded Norovirus.
Consumer Reports recently released a report detailing the many illnesses we can get from a "refreshing" dip in a pool on a hot day. The most common illnesses related to swimming is Cryptosporidium, or Crypto for short, which is spread from fecal matter. Regular levels of chlorine won't kill Crypto and the bacteria can survive in a well-maintained pool for up to ten days. Just swallowing one mouthful can get you sick for weeks. If you get fecal matter in your pool, the only way to truly kill Crypto is to have a professional super-chlorinate the water.
Read more from Consumer Reports here.