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Equipment malfunction during storm leads to overflow at King County’s Sweyolocken Pump Station


King County is investigating the cause of an equipment malfunction at a pump station that led to a wastewater spill into Lake Washington on Feb. 12.


Crews are investigating an equipment malfunction at King County’s Sweyolocken Pump Station at 3100 Bellevue Way SE, Bellevue, that led to a wastewater overflow into Lake Washington in the early morning of Feb. 12.

The unmanned pump station went out at approximately 2:11 a.m. on Tuesday, Feb. 12. An initial investigation by the Wastewater Treatment Division determined that an error in the pump station’s warning system mistakenly characterized the station problem as a low priority malfunction, delaying the response by several hours. 

Once the alert was reviewed and correctly determined to be a high priority, a King County wastewater operator responded quickly to the pump station and reset operations.

Normal pump station operations resumed at 5:45 a.m. 

Preliminary estimates are that up to 750,000 gallons of wastewater overflowed into Lake Washington at Mercer Slough. King County reported the overflow to health and regulatory agencies, is monitoring water quality and has posted signs warning people to avoid contact with the water over the next several days as a precaution to protect public health. 


DNRP Newsroom

Norm Mah, 206-263-0195

About the King County Wastewater Treatment Division
King County’s Wastewater Treatment Division protects public health and enhances the environment by collecting and treating wastewater while recycling valuable resources for the Puget Sound region. The division provides wastewater treatment services to 17 cities, 17 local sewer districts and more than 1.7 million residents across a 420-square-mile area in King, Snohomish and Pierce counties.