Giardiasis (sometimes called Beaver Fever) is an intestinal disease caused by girdia lamblia, a protozoan. Associated symptoms include chronic diarrhea, abdominal cramps, bloating, fatigue, and loss of weight. Treatment by a physician is necessary to kill the organisms and produce a cure.

Giardia is carried by humans and some domestic and wild animals. They get into surface water (lakes, streams, and rivers) and contaminate water supplies. Although isolated waterpockets may appear to be safe, there is no way to be sure that they are. Therefore, it is best to purify all water. It is reommended that whenver possible, only tap water which has been treated, be used for drinking. Water disinfection chemicals are not considered as reliable as heat in killing Giardia. Backcountry surface water should be boiled for one minute. The evening meal is an ideal time to boil water for drinking and brushing teeth for the next day's use.

The three recommended methods for water purification are boiling, chemical treatment, and filtration. Any of these methods should remove giardia, provided you use them properly (some contaminants, such as viruses, cannot be removed by filtration).

The simplest and most reliable method of purification is boiling: bring water to a full rolling boil for at least one full minute. If you use a chemical treatment, such as chlorine or iodine, be sure to use the proper amount for the given water conditions (such as turbidity and temperature). If you develop giardia symptoms, see your physician immediately.