CSO Advisory: North Portland heavy rains lead to localized combined sewer overflow

News Article

October 13, 2023 Update: This advisory has expired.

Heavy rain over North Portland led to a combined sewer overflow around 5:15 p.m. Tuesday that lasted about 16 minutes. The overflow occurred simultaneously to the Willamette River near Cathedral Park and to the Columbia Slough near N. Upland Drive. No other areas of the river are affected. 

Big pipe tracker showing levels peaking at 41% during the storm, dropping to 1% by Oct. 17, 2023 at 3 pm
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As a precaution, Environmental Services advises the public to avoid contact with the river downstream of Cathedral Park for 48 hours because of the possibility of increased bacteria in the water. People recreating on the Columbia Slough also are advised to avoid contact with the water for 48 hours.

Environmental Services adds that people fishing either wait for the end of the advisory period or wash their hands thoroughly if exposed to river water. 

The overflow occurred after a rain burst dropped more than a half-inch in an hour last night in North Portland. 

A combined sewer overflow (CSO) is about 80 percent stormwater and 20 percent sewage. CSOs are rare and can occur during periods of heavy rain or snowfall. Since completing the Big Pipe project in 2011, the number of CSOs have dropped by 94 percent to the Willamette River and more than 99 percent to the Columbia Slough. 

This is the third incident in 23 years to affect the Slough and the first overflow to the river since May. 

People may continue to follow the levels of the Big Pipe system as it directs rainwater and sewage to the City’s main treatment plant. 

About Environmental Services

Environmental Services - the City of Portland’s sewer and stormwater utility - protects public health and environment by collecting and recovering resources from the city’s wastewater, managing stormwater, and restoring and protecting Portland’s rivers, streams, and watersheds.


Diane Dulken

Public Information Officer