Although Washington’s backcountry lakes and streams may appear clean, you could be risking a debilitating sickness by drinking untreated water. The protozoan Giardia lamblia is found throughout the state, spread by both humans and animals (including beaver, hence the nickname “Beaver Fever”). This parasite usually takes up to a week after contact to present itself, and the cramping, nausea, and diarrhea can last up to 25 days.

The disease is curable with drugs, but it’s always best to carry safe drinking water on any trip, or to boil any water taken from creeks or lakes. Bringing water to a full boil is sufficient to kill Giardia and other harmful organisms. Another option—most folks choose this one—is to use a water filter (available in camping stores). Note, however, that these may not filter out other organisms such as Campylobactor jejuni, bacteria that are just 0.2 microns in size. Chlorine and iodine are not always reliable, taste foul, and can be unhealthy.

If you think you have picked up Giardia, be sure to see a medical professional immediately. It’s seldom life-threatening but can cause long-term health damage if left untreated.