Cryptosporidium, or Crypto for short, causes nasty diarrhea when it makes its way to a human host. It can live for more than 10 days even in water treated with chlorine. Between 2011 and 2012, there were 90 outbreaks and almost 1,800 cases in 32 states and Puerto Rico, according to the CDC report. Crypto was determined to be the cause of more than half of these, a dramatic increase since the parasite was first reported in recreational water use in 1988. Most of these cases were in treated water, like pools or spas, but some were in the ocean where people swim. In 2011 and 2012, 73 people were hospitalized, and one person died as a result of the outbreaks.