Mercer Island Crews Stop Sewage Overflow
City of Mercer Island Sewer Utility workers quickly stopped a sanitary sewer overflow at a sewer pump station off of East Mercer Way this morning. Upon identifying the overflow, staff took immediate measures to stop the discharge into Lake Washington at 9:30 AM.
At approximately 7:30 AM on April 9, 2025, during a routine check of the City's Supervisory Control and Data Acquisition (SCADA) system, staff determined that a blockage occurred between the City's sewer catch basin and a sewer pump station around 3:00 PM on April 8, 2025.
This blockage caused a sewer catch basin to surcharge and emergency relief overflow into a 12-inch diameter pipe, which outfalls into Lake Washington approximately 145 feet offshore. The City estimates the overflow rate was 37.5 gallons per minute over an 18-hour period (from 3:30 PM on April 8 to 9:30 AM on April 9), resulting in an estimated total discharge of approximately 40,500 gallons of combined stormwater and wastewater.
The City quickly reported the overflow to Public Health – Seattle & King County and the state Department of Ecology. At the recommendation of Public Health – Seattle & King County, the following beaches and public beach access areas will be closed until April 16, 2025 at 3:30 PM:
- Luther Burbank Beach
- Fruitland Landing
- Mercer Island Boat Launch
- SE 40th Street Landing
- Enatai Beach in Bellevue
Signs will be posted in these locations for at least seven full days to warn the general public against coming into contact with water possibly contaminated with sewage.
In addition, the City is notifying the Mercerwood Shore Club, Covenant Shores, and residents of homes along the eastern shoreline included in the potential area of impact to warn them against coming in contact with water possibly contaminated with sewage until April 16, 2025 at 3:30 PM using door hangers.
