Another unsavory aqua lurker is the giardia parasite, which causes the diarrheal disease giardiasis. More diarrhea, fun. Giardia is a parasite that lives in the intestines and is passed on through poop, and it can survive up to 45 minutes even in the most highly chlorinated pools. Once infected with giardiasis, get ready for lots of lower intestinal backlash in the form of diarrhea, gas, greasy, floating stool (which is infinitely more gross than regular, non-floating stool), cramps, and dehydration.
This aquatic antihero is a disease caused by a group of bacteria called shigella, and most who are infected with shigella develop -- you guessed it -- diarrhea. Add to that list a fever and stomach cramps that usually start a day or two after exposure. Shigella will clear itself up in five to seven days, and some people who are infected may not have any symptoms at all.