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Environmental Services

working for clean rivers

Phone: 503-823-7740

Fax: 503-823-6995

1120 SW 5th Avenue, Room 1000, Portland, OR 97204

More Contact Info

Combined Sewer Overflow (CSO) Information

  • Portland finished construction in 2011 to control combined sewer overflows (CSOs)

  • CSO construction took 20 years and the city finished it on time and on budget

  • CSO construction reduced overflows from about 50 a year to only four or five

  • Today only the heaviest rain storms can cause an overflow

  • News advisories and signs warn the public of CSO events

  • Green streets and rain gardens keep stormwater out of the big pipe system

sewer construction in 1917Why Portland has Combined Sewers

When the City of Portland began constructing sewers in the late 19th century, sewer pipes carried stormwater, sewage and industrial waste - all combined in the same pipes - directly to the Willamette River and Columbia Slough without treatment.
Watch the CSO program video for more 


2013 Willamette River Big Float

Enjoy the River

Thanks to the CSO control program, the Willamette River and Columbia Slough are cleaner than they've been in generations. Willamette River water today is safer for swimming.
Check the Willamette recreation index for E. coli and temperature information


Expo Center rain gardenGreen Infrastructure

Portland uses rain gardens, green street planters, and other green infrastructure to keep stormwater out of combined sewers and ensure that the Big Pipes continue controlling overflows now and for generations to come.
Learn about green street planters, ecoroofs and other green infrastructure