Waterborne illness, however, is not solely associated with disasters or lesser developed countries. Swimming in lakes, streams, and improperly chlorinated pools can expose individuals to parasitic infections. According to the CDC, recreational water illnesses occur when individuals swallow infected water from pools, hot tubs, streams, lakes, and even the ocean. Giardia and Cryptosporidum are two specific parasites, which can cause diarrhea in infected invididuals. Shigella and E. coli can also be found in many different bodies of water. Shigella and E. coli can also cause diarrhea. Cryptosporidium can be potentially deadly in certain individuals whose immune systems are not strong enough to fight the parasite. E. coli infections can develop into a more serious complication known as Hemolytic Uremic Syndrome (HUS). HUS is particularly serious in young children, the elderly, and individuals with compromised immune systems. Individuals who swim in these waterways or drink improperly filtered water can ingest these bacteria and parasites.  Ensuring the safety of pools has become additionally complicated as parasites and bacteria evolve and become resistant to chlorination products.