Grand Canyon National Park officials are warning that E. coli bacteria has been detected in the water supply near Phantom Ranch, the only lodging at the bottom of the canyon.
Park authorities warn visitors not to consume any water in that area without boiling it first.
Phantom Ranch and the immediate vicinity are the only areas of the park reported to be affected.
E. coli's presence can be caused by increased run-off from heavy rains, which the area saw because of the remnants of a tropical storm. It usually indicates human or animal waste contamination.
Park officials have not determined the source of the bacteria and are also chlorinating the water.
