Associated Press

BAKER CITY, Ore. - Baker City officials have shut off another source of city water as a result of a positive test for cryptosporidium, the parasite that sickened many residents.

The discovery this week of cryptosporidium in water from a mountain stream named Elk Creek adds to the mystery over the contamination, The Baker City Herald reported.

The parasite causes severe diarrhea. State and local officials say 300 to 400 people were ill.

Animal feces is the usual source of cryptosporidium. When the illness started in late July, the city suspected water from a lake where mountain goats congregate and stopped drawing from it.

Much of the city's water comes from diversions from streams such as Elk Creek. Public Works Director Michelle Owen, the city's watershed manager, inspected the Elk Creek diversion July 31 and found no evidence cattle had been in the area. She said the namesake animals, elk, are known to roam the upper part of the creek's drainage.

City officials said they're increasingly concerned about adequate supplies and have asked water users to be sparing.

They've also advised residents to boil water used for drinking and tooth care.

Dr. Bill Keene, the senior state epidemiologist, said that if the city's water is determined to be the source of the cryptosporidium, the most plausible theory, the outbreak would be the largest in a municipal water system since 1994 in Las Vegas.

And if mountain goats turn out to be the cause, that might be a first in the United States, he said.

The city faces a 2016 federal deadline to protect the city water against cryptosporidium, likely by treating it in a plant with ultraviolet light.

The city council learned this week that because of the outbreak, it may have to build a more expensive filtration plant.