G. lamblia, also known as Giardia duodenalis or Giardia intestinalis, is a flagellated enteric parasite that has two forms during its life cycle. In the early stages, giardia exists as a flagellated trophozoite in the small intestines and then forms into a cyst as it passes through the colon. The cyst is relatively resistant to chlorination and ozonolysis explaining why it is the most common cause of outbreaks of diarrheal illness due to drinking water.

Giardiasis is also one of the leading causes of food and waterborne diarrhoea throughout the world. Individuals contract giardiasis by consuming contaminated food and water containing the giardia cyst. Some symptoms associated with giardiasis include but are not limited to diarrhoea, malaise, flatulence, foul-smelling greasy stool, and abdominal cramps. Infections can last from several days or several weeks if left untreated.