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Combined sewer overflows now reported live, online


Kayakers, boaters, swimmers, and others now have a new resource to help them make informed decisions about using Seattle’s waterways.


City of Seattle logo King County logoKayakers, boaters, swimmers, and others now have a new resource to help them make informed decisions about using Seattle’s waterways. King County and City of Seattle have collaborated on a website to provide the public with real-time information and status updates on combined sewer overflows (CSOs) that have occurred due to heavy rain. To view the map, go to or

Combined sewer overflows occur in older parts of Seattle where pipes handle both sewage and stormwater in order to prevent backups into homes and streets during heavy rains. King County manages 38 CSO outfall locations and Seattle manages 90.

During the CSO discharge, and for 48 hours afterward, people are at risk from exposure to bacteria in the water near the overflow outfalls. The County and City website will update the CSO web information at least hourly, and in many cases every 10 minutes, to provide the fastest notification possible. More than half of the 128 sites are connected to a phone line that enables display of the real-time information. Data for the other sites is collected weekly.

Combined sewer overflows (CSOs) are usually limited to discharge in the winter between October and May when Seattle receives heavy rain. They may also occur during summer months, particularly during or after intense rainfall. Signs are posted at CSO outfalls on shorelines.

Monthly and annual reports about overflows are also available at and clicking on “Library or at by clicking on “Reports & Regulations”.

Both King County and City of Seattle are committed to controlling CSOs to protect public health and the environment. Both are working with state and federal regulators to comply with the federal Clean Water Act.

Note to editors and reporters: Visit the WTD Newsroom, a portal to information for the news media about the Wastewater Treatment Division, King County Department of Natural Resources and Parks:


About King County
People enjoy clean water and a healthy environment because of King County's wastewater treatment program. The county’s Wastewater Treatment Division protects public health, the environment and the economy by serving 17 cities, 17 local sewer districts and more than 1.5 million residents in King, Snohomish and Pierce counties. Formerly called Metro, the regional clean-water agency now operated by King County has been preventing water pollution for nearly 50 years.

About Seattle Public Utilities
In addition to providing a reliable water supply to more than 1.3 million customers in the Seattle metropolitan area, SPU provides essential sewer, drainage, solid waste and engineering services that safeguard public health, maintain the City’s infrastructure and protect, conserve and enhance the region's environmental resources.

Related information

Combined sewer overflow status

Combined Sewer Overflow Control Program

King County Wastewater Treatment