PORTLAND, Ore. (KOIN) — A “combined sewer overflow advisory” is in effect for the Willamette River after heavy rainfall from Monday’s atmospheric river overwhelmed Portland’s sewer system, causing a mix of sewage (20%) and rainwater (80%) to spill into the Willamette River, downstream of Willamette Park.

According to the Portland Bureau of Environmental Services’ “big pipe tracker,” Portland’s sewer system reached maximum capacity at 1:15 p.m. and officially began spilling into the Willamette by 1:30 p.m. People are advised to avoid the river due to the spill.

“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 has said during past spills. “The river’s water quality is safe for recreation during all other times.”

In 2011, Portland completed its “big pipe” system: a $1.4 billion upgrade to its sewer system that now stores and transports larger amounts of water and sewage to the city’s wastewater treatment plant in North Portland. Since its completion, the City of Portland says that the “big pipe” system has reduced Willamette sewage overflows by 94%. However, spills can still occur during periods of excessive rain and snow.