PORTLAND, Ore. (PORTLAND TRIBUNE) — Portland will return to the Bull Run Reservoir as its primary water source on Wednesday, March 15.

That is only one week after the potentially deadly parasite Cryptosporidium was found in a sample of water drawn from the reservoir. Water and public health officials insist the risk of anyone getting sick from drinking Bull Run water is extremely unlikely, however, although they advise people with compromised immune systems to consult with their doctors.

“Our top priority is to protect public health,” said Water Bureau Administrator Mike Stuhr. “The evidence and data collected, along with input from our partners with the Multnomah County Health Department and regulators at the Oregon Health Authority, indicates the risk remains low.”

Crypto, as the parasite is commonly called, has been found 13 times in Bull Run water since the beginning of the year. The most recent finding was in a sample drawn on March 8. Additional positive findings are likely. But state and county health officials insist the general public is not at risk because the amount found has been so low.

Neverthless, the Portland Water Bureau took the reservoir offline and switched over the groundwater wells along the Columbia River owned by the city on Feb. 13. They gave been providing all of the water to the city customers since then.

Crypto is found in animal feces. It can cause cryptosporidiosis, a respiratory and gastrointestinal illness. The illness can affect anyone, but is especially dangerous to immunodeficient people. An outbreak killed 104 people and sickened thousands of others in 1993 in Milwaukie, Wisconsin.

The outbreak prompted the U.S Environmental Protection Agency to adopt a rule requiring cities with open water sources like Portland to treat for crypto. The OHA granted Portland a variance because Bull Run water has been so historically clean.

But the variance requires the bureau to monitor for crypto and report it fundings. The OHA has the authority to cancel the variance and order the bureau to build a plant to treat for crypto, which could cost $385 million or more. It would be financed by water customers, inlcuding those outside of Portland.

Customers with questions are encouraged to call the Water Line at 503-823-7525.The Portland Tribune is a KOIN media partner.