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Combined sewer overflow status

This site is a joint effort by King County and the City of Seattle.

For questions about the King County Protecting Our Waters Program, please contact John Phillips.

For questions about the City of Seattle Sewage Overflow Prevention Program, please contact

What's happening in your waterway? Current CSO information to inform your choices

Overview map -- click on region to view detail map

Combined Sewer Overflow Locations: Seattle
Combined Sewer Overflow Locations: Seattle
Combined Sewer Overflow Legend: Seattle
NW Seattle CSO Status NE Seattle CSO Status NW Seattle CSO Status NE Seattle CSO Status SE Seattle CSO Status SW Seattle CSO Status

King County and the City of Seattle are piloting this website to inform the public when and where CSOs are occurring or have recently occurred. The purpose is to give the public information so that the public may make informed decisions about where and how to use our local waters. CSOs usually discharge in the winter between October and May, but may discharge during very intense rainfall in the summer and early fall. During the discharge and for at least 48 hours following the discharge the public should avoid fishing, wading, swimming, boating, or other contact with the water near the CSO location to avoid potential public health risks.

Click on a region to view CSO status

This map shows the 38 CSOs operated by King County (designated K###) and the 90 operated by Seattle (designated S###). Most of the locations have real time information available from computerized systems that monitor and operate the wastewater system. The data for some CSO locations are manually collected or intermittently available due to sporadic transmission interruptions. The CSO status will always be listed as “Real time data not available” where data is manually collected. CSO sites with no updated data available within the previous 12 hours due to transmission interruptions will be marked as “Real time data not available” until more current data is transmitted. The CSO status information on this page is updated with available data every 10 minutes for the County sites, and every 60 minutes for Seattle sites.

DISCLAIMER: Because of the desire to relay information as soon as practicable, this status has not yet been reviewed by King County or Seattle staff. Consequently, King County and Seattle cannot guarantee the accuracy of the information found on this website. Reviewed and updated data is reported in monthly and annual reports to the Washington State Department of Ecology. These reports are available to the public. King County’s annual reports can be found on their website and Seattle’s annual reports can be found on their website.