Giardia is a microscopic parasite that causes an intestinal infection known as giardiasis, typically transmitted through contaminated water, food, or close personal contact. It is commonly spread by drinking untreated water from lakes or streams, consuming contaminated food, or through poor hand hygiene. Symptoms often include watery diarrhea, abdominal cramps, bloating, gas, nausea, fatigue, and weight loss, though some infected individuals may have no symptoms. The infection can be acute or become chronic if untreated, leading to prolonged digestive disturbances. Diagnosis is confirmed through stool testing, and treatment usually involves prescription antiparasitic medications. Preventive measures include proper handwashing, safe water practices, and avoiding ingestion of untreated water during travel or outdoor activities.