The Portland Water Bureau has found the dangerous microorganism cryptosporidium in the region’s primary source of water.

Crypto was found in samples taken this week at the Bull Run Watershed, a reservoir complex near Mount Hood. The water bureau has found crypto in samples every month since October. 

The microorganism can cause gastrointestinal problems and can be especially dangerous for people with weakened immune systems. It’s usually caused by animal feces entering the water system.

Portland does not treat its water supply for crypto right now. But to abide by state and federal regulations, the city is building a filtration plant that will protect against crypto and other potential problems.

The plant will cost at least $500 million and come online in 2027.