URGENT ADVISORY: Sewer Lakeline Blockage, Request to Cease Wastewater Discharge

Updated: 02/24/2026, 11:00 a.m.

Area Affected: Properties located in North Mercer Island, from Luther Burbank Park to 97th Ave SE. (see map; scroll for list of affected addresses) Text "SewerFeb2026" to 38276 to be added to a text alert notification system for urgent updates.

Urgent Action Required

Due to a blockage in the underwater sewer lakeline between Pump Station 10 and Pump Station 11 on the north end of Mercer Island, properties in the area denoted on the map are currently unable to discharge wastewater to the sewer system. The City requests all property owners in the affected area immediately cease all wastewater discharge. Every gallon of wastewater discharged—whether from showering, laundry, dishwashing, or flushing—fills the limited capacity remaining in the sewer pipes serving these properties. Because there is currently no outlet, this wastewater has nowhere to go and may begin backing up.

The sewer pipe serving these properties is likely equipped with check valves designed to prevent backflow from the City sewer line. These valves are likely closed due to the blockage in the lakeline. This means that the wastewater from these properties is being “held” in the sewer lines serving the property and has nowhere to go. Once these sewer lines are completely full, wastewater will back up into homes.

Please immediately STOP any activities that result in wastewater discharge, including running washing machines and dishwashers, and taking showers/baths. Try to minimize toilet flushing.

The water distribution system that provides drinking water to your home is NOT affected or tied to the sewer system. Your water is safe to drink.

What The City of Mercer Island Is Doing

City crews are working around the clock to address this complex situation:

• Emergency Relief: The City has contracted third-party Vactor trucks to pump out excess wastewater from the system to create temporary capacity while crews are working to clear the blockage.
• Access Challenges: The blockage is located within the submerged lakeline with no manhole access, making repairs difficult. City crews have determined the blockage is in a section of the lakeline east of Covenant Shores and have narrowed it to a 1,000-foot section of the line. City crews are working this morning to access the lakeline from an on-shore access point with vactor equipment to remove the blockage.
• Facility Closures: For the safety of the public and to reduce the load on this section of the sewer system, all restrooms at Luther Burbank Park are currently closed.

Status Updates: The City understands the severe impact of this situation on property owners and will provide updates as the work progresses to clear the blockage. Another update will be provided as soon as the blockage is cleared or by 3 p.m. if the City is unable to make progress on clearing the line. If you experience a sewer issue at your property or have immediate concerns, please contact our Customer Service team at 206-275-7600.

We appreciate your immediate cooperation in ceasing wastewater discharge at your property while City crews work to resolve this emergency.