Giardia lamblia is a microscopic parasite found in contaminated water. It causes intestinal illness and enters water through feces of infected animals or humans.

Giardia lamblia is a resilient, single-celled parasite that forms protective cysts. It's commonly found in untreated surface water sources like lakes and streams. Giardia is resistant to chlorine disinfection, making it challenging to eliminate through standard water treatment. Water systems test for Giardia by filtering large volumes of water and examining for cysts under a microscope. Proper water treatment, including filtration and UV disinfection, is crucial for prevention, along with good hygiene practices.