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The City of Portland, Oregon

Environmental Services

working for clean rivers

Phone: 503-823-7740

Fax: 503-823-6995

1120 SW 5th Ave, Suite 613, Portland, OR 97204

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Summer combined sewer overflow (CSO) warnings begin

Summer combined sewer overflow (CSO) warnings begin

May 16, 2011

For more information contact Linc Mann, 503-823-5328

Today, the City of Portland begins its River Alert public notification program for summer combined sewer overflows (CSOs). Between mid-May and mid-October, the city sends a CSO advisory to Portland media each time Portland’s combined sewer system overflows to the Willamette River.

This will be the River Alert program’s final summer notification season. After Portland completes its 20-year CSO control program this winter, Environmental Services will issue alerts for all CSO events year-round. Completing the program will reduce the number of CSO events from about 50 each year to an average of four events every winter and one event every third summer.

The city recommends that for 48 hours after a CSO event ends people avoid activities in the river during which water could be swallowed.

A CSO advisory extends for 48 hours after rain has stopped. People who fish when the advisory is in effect should wash their hands following contact with the water. Those who choose to eat fish caught in the Willamette River when an advisory is in effect should cook fish thoroughly to kill bacteria.

Because of recent rain, the 2011 summer CSO notification season starts today with a CSO advisory in effect.

River Alert Program

Between mid-May and mid-October, notifies the public each time rain causes a CSO event. The summer notification season begins today with a CSO advisory in effect and warning signs open on the Willamette River.

These are the components of the River Alert program:


  • Environmental Services issues a CSO advisory to local media.
  • Environmental Services opens signs at public access points along the river to warn river users of CSOs.
  • The signs display the River Alert hotline number, 503-823-2479. The hotline is available 24 hours a day with a recorded message to let callers know if a CSO advisory is in effect.
  • The Oregonian newspaper publishes CSO warning notices and the River Alert hotline number on its weather page.
  • Permanent red and white signs identify outfall pipes along the Willamette River and Columbia Slough where combined sewers could overflow.


CSO Improvements to Date

  • In October 2000, Environmental Services completed construction of the Columbia Slough Big Pipe to eliminate CSOs to the slough.
  • In December 2006, the city completed the 3.5-mile, 14-foot diameter West Side Big Pipe and the Swan Island CSO Pump Station. The West Side Big Pipe captures stormwater and sewage from the west side of the Willamette River during rainy weather.
  • In October 2010, the city completed tunneling the nearly six-mile long, 22-foot diameter East Side Big Pipe. Environmental Services will activate the pipe this winter. 

There will be CSOs during rainstorms until all CSO projects are complete this December. After December 2011, Portland’s combined sewers will overflow to the Willamette River an average of four times each winter and once every three summers.