PORTLAND, Ore. -- The city of Portland is throwing in the towel in the battle to keep from treating Bull Run water for the parasite Cryptosporidium.

The pristine Bull Run watershed sits 26 miles east of Portland in the Mt. Hood National Forest. Its two reservoirs hold 17 billion gallons of drinking water used by 950,000 people in the greater Portland area.

The water is treated with chlorine, but not filtered, and considered some of the cleanest water in America.

That's what allowed Portland to avoid EPA regulations, started back in 2006, which would have forced the city to build a treatment plant to get rid of the parasite. It can cause diarrhea and other issues.

But those days are over.

“Short of having Congress revisit the rule, I think we’re going to have to comply with it,” said Portland Commissioner Nick Fish.

Read more: FAQ about Cryptosporidium

Several people on the streets of Portland agreed.

“That natural purity is great. But when there’s a health concern that could impact many lives then that’s sort of a different issue,” said Melissa Jacobs.

The city reported that testing found the parasite 19 times in samples taken from the watershed between January and March of 2017.

A letter from the city to the Oregon Health Authority stated, “Although the source is assumed to be wildlife scat, the type of wildlife is currently unknown.”

Many had heard that city testing discovered the parasite. It’s changed the way some think about Portland’s water.

“Portland’s got this great water and you don’t have to worry about buying bottled water—but guess what? It’s not so great,” said Mike Stringer.

Fish said the contamination likely came from animals that pooped near the edge of the water and it was pushed into the reservoir by the winter's heavy rains.

It’s unclear what city leaders will do next. A presentation to the city six years ago estimated getting the parasite out would cost $100-350 million. Ratepayers will foot the bill according to Fish, maybe as early as July of 2018, depending on what the council decides to do.

When asked how the water could be at such risk that it requires a treatment plant to get rid of the parasite but is still safe enough to drink in the meantime, Water Bureau Communications Director Nicole Adams said the public health risk remains low.

“Public health data showed there were no incidents of Cryptosporidium-related illnesses attributable to the water during the time of detections [or before, or after].”