City of MI lifts wastewater restrictions for affected properties

Published 9:30 am Wednesday, February 25, 2026

For nearly nine hours on Feb. 24, numerous north end Mercer Island properties were affected by a sewer lakeline blockage and residents were urgently advised to halt activities resulting in wastewater discharge.

In the 11 a.m. city social media post, impacted residents situated in areas near Luther Burbank Park and along North Mercer Way and 97th Avenue Northeast were notified to immediately stop running their washing machines and dishwashers, refrain from taking showers/baths and try to minimize toilet flushing.

The blockage occurred in the underwater sewer lakeline between Pump Station 10 and Pump Station 11. The city said that every gallon of wastewater discharged from the above activities fills the limited capacity remaining in the sewer pipes serving these properties. With no current outlet, the wastewater was being “held” in those sewer lines with nowhere to go and could have begun backing up into homes.

Impacted Islanders’ water was safe to drink during this juncture since the water distribution system is not affected or tied to the sewer system.

At 8:15 p.m. that evening, after the Mercer Island Public Works crew had successfully cleared the blockage, the city lifted the “Cease Wastewater Discharge” advisory for all impacted properties and added that Pump Station 10 resumed activity after a temporary valve shutdown to drain a portion of sewer line.

It was difficult and time-consuming work, the city said, noting that residents could resume normal usage of showers, toilets, dishwashers and washing machines.

During the blockage, Public Health – Seattle & King County issued an advisory that people should avoid contact with Lake Washington in the impacted area; as a standard safety precaution, the advisory will remain in effect for the next week, according to the city.

“The sewer lakeline is a complex piece of underwater infrastructure with very limited access, which presents immense challenges when a blockage occurs,” said Jason Kintner, chief of operations and public works director. “The city of Mercer Island’s Public Works crew did a sensational job working with urgency to gain access to the line so we could clear the blockage as quickly as possible. We are also grateful for the cooperation from residents in the affected area, who heeded our request to limit discharges of wastewater. This provided crucial relief to the sewer line, helping our crews locate and clear the blockage.”

The massive workload toward blockage clearance featured crews operating from both ends of the impacted lakeline section and included pressure draw-down to place sewer equipment closer to the blockage location and usage of a 1,000-foot high-pressure water line.

“Ceasing wastewater discharge in the affected area is helping city crews resolve this issue faster. The community’s rapid response today has helped limit new wastewater from entering the system allowing for pressure to be successfully drawn down. Thank you for doing your part to help us,” said the city, adding that the Mercer Island Community and Event Center was open until 9 p.m. for residents needing to utilize restrooms and shower facilities.

As always, the city’s customer service team was available to receive calls from Islanders who experienced a sewer issue.

It was the city’s second wastewater incident in February. After MI crews responded to an overflow in the 9000 block of Fortuna Drive at about 5 p.m. on Feb. 7, the King County Wastewater Treatment Division crews arrived at 7:45 p.m. to help work on the situation.

“An initial investigation determined that a temporary bypass system collapsed near the intersection of Fortuna Drive and North Mercer Way, causing wastewater to back up and overflow from a maintenance hole,” reads the King County site. “The bypass system was installed as part of our ongoing North Mercer Island/Enatai Sewer Upgrade Project, where crews are replacing aging pipes.”

King County and MI crews stopped and contained the overflow at approximately 1:15 a.m. on Feb. 8 and the construction contractor completed repairs and restored normal operations at the site by noon that day.

A Public Health – Seattle & King County advisory instructed the public to avoid contact with potentially contaminated water in the area until 1:15 a.m. on Feb. 15, or until the advisory was lifted, according to the King County site.