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Combined sewer overflows (CSOs) are relief points in older sewer systems that carry sewage and stormwater in the same pipe. When heavy rains fill the pipes, CSOs release sewage and stormwater into rivers, lakes, or Puget Sound.

In King County, CSOs are only located within the City of Seattle. King County and the City of Seattle are working together to control CSOs and keep sewage and stormwater out of local waterways.

kayakers
CombinedSewer-Title_500 Why does sewage overflow on the rainiest days? Find out about the history of CSOs in Seattle.
Storage tank Learn about  traditional solutions to fixing the problem.

Erika Peterson
Water Quality Project Manager

206-477-5525