Source: Water can become contaminated when in contact with animal waste, agricultural runoff, or when it contains animals that are infected with the Giardia parasite.
Summary: Giardia Lamblia is a single celled (protozoa) parasite that lives in the digestive tract of animals and results in intestinal infection and diarrhea complications. Giardia is spread through fecal matter, and can be spread to many things that come in contact with feces. Infection takes place when the parasitic cyst is consumed and it replicates in the digestive tract. 1-10 billion cysts can be produced daily in an infected person. Drinking untreated lake or river water can lead to an infection. Giardia can live for multiple months in water and is resistant to chlorine disinfection processes.