Giardiasis (pronounced "jee-ar-DYE-uh-sus"), or giardia, is an infection of the intestines caused by the parasite Giardia lamblia. You may become infected with giardia if you eat food or drink water that is tainted with human or animal waste. You can also get giardia by coming into close contact with an infected person. The illness is most often a problem in developing countries where tap water is not safe; but you can get giardiasis in developed countries, too. In the U.S. and Canada, you can get giardia by drinking untreated water from wells, streams, rivers, and lakes. This is true even in mountain lakes and streams, where the water may seem pure. Follow the links below to find WebMD's comprehensive coverage about how giardiasis is contracted, what it looks like, how to treat it, and much more.