The water may look clean, but hikers and campers should avoid drinking untreated surface water.

This summer, a youth camp director told me that during field trips, campers often ask if the water in a crystal-clear mountain brook is safe to drink.

While the water appears clean, the answer is still “NO – absolutely NOT!” The reasons why require a field trip upstream. Warning to the squeamish - or those finishing breakfast – this sojourn includes an excursion to your small intestine.

 Freshwater streams even in the most pristine, forested watersheds contain a microscopic "protozoan" named giardia lamblia, an intestinal parasite found in mammals. If you're a hiker or camper, you've likely heard of “beaver fever,” an infection in the small intestine medically termed "Giardiasis.”

Incubation time between ingesting the parasite and developing gastric distress is 7 - 14 days and the acute phase lasts 2 - 4 weeks. Symptoms include cramps, diarrhea, gas, headache, fever, and nausea.

Giardia occurs in lakes and streams where water-dwelling animals such as beavers and muskrats, or wading domestic animals cause contamination. Hikers are at risk if they drink untreated water. Travelers risk giardiasis in regions where water supplies become contaminated by sewage.

Prevention is simple: purification by boiling, filtration, chlorination or iodine treatments.

All surface water sources should be considered as potentially contaminated. While beavers and muskrats are most often cited, wading deer and moose also carry Giardia.

People are in the parasite food chain. Mammal digestive tracts are habitat for Giardia. Finding their way there is "business as usual" for the tiny protozoan.

Best advice? Don’t drink the water!