Heavy rains returned to Portland last week. Now cryptosporidium has, too.

The Portland Water Bureau announced this afternoon that it detected crypto—a parasitic microorganism that in some forms can lead to serious health problems in humans—in a water sample taken from the Bull Run watershed on September 24.

"At this time, the bureau and public health partners at Multnomah County continue to believe Bull Run water is safe to drink," PWB Administrator Mike Stuhr said in a news release.

The detection of crypto relatively shortly after last week's heavy rains bolsters the theory that this year's obscenely wet winter is what led to 19 detections of crypto in the water supply from January to March. Those detections came rapid-fire after years of mostly crypto-free results, and led officials to surmise that downpours were washing animal waste into the water supply.

The crypto detections also put Portland out of compliance with a deal they'd struck with federal regulators in 2012 that allowed the city not to treat for the parasite. And that, in turn, led Portland officials to green light a massive filtration plant that will cost as much as $500 million, under current estimates.

As we wrote in May, that filtration plant is far, far more than Portland would need to battle cryptosporidium (a UV plant that deactivates the threat would cost something like $105 million). But officials approved the filtration plant anyway, basically under the theory that there's no sign that crypto is an actual problem for Portland's water, but that the federal government would force the city to act anyway.

That being the case, the City Council decided to pull out all the stops on a facility that could battle all manner of potential threats. That would include turbidity that could be caused by forest fires in the Bull Run watershed, a possibility that became all the more real when the recent Eagle Creek fire breached the watershed's boundaries.

Activists who frequently battle the city on water regulation have argued the filtration plant is unnecessary, and say the city should continue to press for an exemption to treatment.

Hit the jump for the PWB's full release:

The Portland Water Bureau received results today from a sample collected on Sept. 24 that was positive for Cryptosporidium, a potentially disease-causing microorganism. The detection was from a sample collected from the Bull Run Watershed intake as part of ongoing monitoring for Cryptosporidium. One Cryptosporidium oocyst was detected in this 10-liter sample. This is the first detection since a series of detections spanning from January to March of this year.

The Portland Water Bureau has monitored for Cryptosporidium under conditions of a variance for the treatment of Cryptosporidium issued by its regulators at the Oregon Health Authority. As a result of the detections earlier this year, the Oregon Health Authority (OHA) informed the Portland Water Bureau that the variance from treating for Cryptosporidium would be revoked no later than Nov. 22, 2017. On Aug. 2, City Council directed the bureau to construct a water filtration plant to meet the Cryptosporidium treatment requirements. The Portland Water Bureau will submit a schedule for construction of a filtration plant and ongoing measures to continue to protect public health to OHA by Oct. 11.

"At this time, the bureau and public health partners at Multnomah County continue to believe Bull Run water is safe to drink," said Portland Water Bureau Administrator Michael Stuhr. "We will continue to monitor for Cryptosporidium, protect the watershed, notify the public, and work with our health partners to make the best decisions for public health."

As always, the bureau recommends that people with severely weakened immune systems seek specific advice from their health care providers about drinking water. There is no need for the general public to take additional precautions.

"We continually monitor for human illness caused by Cryptosporidium but since past detections of Cryptosporidium oocysts in Bull Run water have not been associated with an increase in human disease, I do not expect it to be different this time," said Multnomah County Health Officer Dr. Paul Lewis.

The bureau will continue to sample the Bull Run for Cryptosporidium; gather information about these detections; and notify its regulators, health officials, and the public of any additional detections.