PORTLAND, Ore. (KOIN) — Heavy post-Christmas rainfall is actively causing a mixture of sewage and stormwater to overflow into the Willamette River downstream of Willamette Park.

The Portland Bureau of Environmental Services announced that the sewage spill began around 10:15 p.m. on Monday, after Portland’s Big Pipe system reached capacity. The sewer runoff, this city says, is approximately 80% stormwater and 20% sewage.

“During an overflow and for 48 hours afterward, the public is advised to avoid contact with the river because of increased bacteria in the water,” the Bureau of Environmental Services said. “The river’s water quality is safe for recreation during all other times.”

Portland’s sewer system reached capacity at approximately 10:15 p.m. on Monday. (City of Portland)

The sewage is overflowing from multiple river outfalls and no estimated time has been given for when the spill will subside. The Bureau of Environmental Services said that these overflows occur approximately four times per winter season and once every three summers, on average. Portland’s latest sewage and stormwater volume can be tracked through the city’s website.

Portland’s $1.4 billion Big Pipe system is a series of major sewer improvements that better stores and transports large amounts of water and sewage to the city’s wastewater treatment plant in North Portland. The project was completed in 2011 after decades of planning and construction. Since its completion, the Big Pipe system has reportedly reduced sewage overflows in the Willamette by 94%. However, these spills can still occur during periods of excessive rain and snow. 

Portland’s Big Pipe system. (City of Portland)

Before the project, incidents occurred [in] the Willamette River an average of 50 times a year, with some lasting days,” the City of Portland said.

The current sewage overflow is the fourth recorded on the Willamette in 2022.