When ingested, they can cause a gastrointestinal disease called giardiasis.
Giardiasis is a frequent cause of diarrhea.
Symptoms may include diarrhea, fatigue, and cramps. Waterborne giardiasis may occur as a result of disinfection problems or inadequate filtration procedures. Cysts are a stage in the life-cycle of some Giardia. In this stage, the Giardia can infect humans and other animals. The effectiveness of treatment technologies are used to judge how well removal works since direct measurement of pathogens in treated water is not feasible.