GRAND CANYON NATIONAL PARK, Ariz. (AP) — Grand Canyon National Park officials warned that E. coli bacteria was detected Friday in the water supply close to Phantom Ranch, the only lodging at the bottom of the canyon.

Park authorities said visitors should not consume any water in that area without boiling it first. E. coli can lead to diarrhea, cramps, headaches and sometimes kidney failure and even death. Infants, younger children and immuno-compromised people are more at risk.

Water from the Phantom Ranch area — including that being used to brush teeth, make ice and prepare food — should be brought to “a rolling boil” for one minute per 1,000 feet (305 meters) of elevation and then cooled before using, officials said.

Phantom Ranch and the immediate vicinity — all reachable only by a long hike or mule ride from the canyon rim or by raft on the Colorado River — are the only areas of the park affected.

Park officials are collecting more sampling to figure out the source of the bacteria and are also chlorinating water in the area again.

E. coli’s presence can be caused by increased run-off from heavy rains or a break in pipes or water treatment. It usually indicates human or animal waste contamination.

The Grand Canyon area recently saw heavy rains brought by the remnants of a tropical storm.