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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

More Contact Info

Combined Sewer Overflow Control (Big Pipe Project)

Portland completed the Big Pipe Project in 2011 to eliminate almost all sewage releases to Portland's Willamette River and Columbia Slough.

Overview: 94% reduction in combined sewer overflows (CSOs) to the Willamette River 
99% reduction to the Columbia Slough
Before CSO control: An average of 50 Willamette River CSO events each year.
Today: An average of four CSO events each winter and one every third summer.

100%: Eliminating all CSOs, instead of 94%, would have doubled the $1.4 billion project cost

CSO volume reductions


CSO videoLesley Stahl narrates Portland's CSO Program, a video overview of Portland's 20-year program to control combined sewer overflows. The overall program became known as the Big Pipe Project. 

downspout disconnectionCornerstone projects - downspout disconnections, sumps, stream diversions and sewer separations - removed millions of gallons of stormwater from combined sewers to allow construction of smaller CSO control facilities.

big pipe constructionBig Pipes - one on the Columbia Slough, two on the Willamette River - intercept combined sewage and stormwater and direct it to the treatment plant.





River Alert

See if a combined sewer overflow (CSO) or sanitary sewer overflow (SSO) advisory is in effect

Check the Rec: Willamette River Recreation Index

Get e. coli and temperature information for the Willamette River in Portland

Combined Sewer Overflow (CSO) Information

Information about Portland's combined sewer system and CSO control

Big Pipes

CSO control tunnels on the Columbia Slough and Willamette River