Signs and symptoms of giardiasis can vary, and some people may be infected without showing any symptoms. Symptoms, when they occur, can last two weeks or longer. The most common symptoms are diarrhea, gas, fatty or foul-smelling stools (they may float), and stomach or abdominal cramping. Nausea and vomiting may occur along with malaise, fatigue, and bloating. The symptoms together can lead to dehydration. Less common symptoms may include itching of the skin, hives, joint swelling, and swollen eyes. If untreated, the infection can persist for months to years. Over time, giardiasis can cause weight loss, malnutrition, and delayed development in children.

Source: http://www.rxlist.com