PORTLAND, Ore. (KOIN) — Samples from the Bull Run Watershed recently tested positive for trace amounts of cryptosporidium, and while health officials say levels of the microorganism do not pose a risk to public health, the news has some questioning whether the city needs to build a new water treatment plant.

The parasite comes from human or animal waste, and at certain levels, it can cause symptoms like diarrhea, dehydration, fever, nausea and vomiting.

Unlike in most cities, the Portland Water Bureau doesn’t treat its water for cryptosporidium. In 2012, the state gave Portland a 10-year exemption from treating its water because the parasite hadn’t shown up in tests for a decade.

But now, at the 5-year mark, traces of cryptosporidium have shown up at the intake pipe in the Bull Run Watershed.

Water samples have tested positive for cryptosporidium 4 times within the past 5 weeks, and more positive tests could force the construction of a water treatment facility that could cost up to $300 million.

Portland Water Bureau Director Michael Stuhr told KOIN 6 News the bureau is in compliance with state regulations, but he has an idea why samples are coming back positive for the parasite.

“We’ve had very, very unseasonable rains, just constant, steady and heavy rains, so instead of a large amount of that scat staying put where it was dropped, some of it washes into the system,” Stuhr explained.

In the past, Stuhr said the bureau believed it had a “pretty pristine” water supply and that “building a big treatment plant operation wasn’t necessary.”

But that could change as the bureau continues to test water samples from the Bull Run Watershed for cryptosporidium 4 times a week throughout the rest of the year.

If samples continue coming back positive for the parasite, Stuhr said the state and Environmental Protection Agency could bring up the idea of a treatment plant.

Meanwhile, the city is already spending over $200 million to build new underground reservoirs to protect drinking water in compliance with EPA requirements.