Giardia is a microscopic parasite that causes an intestinal infection known as giardiasis. It is commonly found in contaminated water, food, or surfaces. People can become infected by drinking untreated water from lakes or rivers, or by consuming food washed with contaminated water. Symptoms of giardiasis include diarrhea, abdominal cramps, and nausea. The parasite is transmitted through the fecal-oral route, meaning it can spread from person to person or through contact with infected animals. Diagnosis is typically made through stool tests, and treatment often involves medications that target the parasite. Maintaining good hygiene and ensuring safe drinking water can help prevent infection.