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Project update

March 15, 2023

*Please note that construction schedules often change due to weather, staffing, and other unforeseen things. Dates on email notices may differ from the dates posted on the web. The dates below will be updated regularly based on updates given by our contractor.

Construction activity in Mercer Island*

At the North Mercer Pump Station: Crews continue pouring concrete for the temporary pump station. See the notification for details and what to expect .

On N Mercer Way: Crews will temporarily close a short section of eastbound North Mercer Way near Fortuna Drive for approximately four weeks. See the notification for details and what to expect .

On SE 24th St: Crews continue installing pipe in the intersection of 78th and SE 24th St. To ensure safety there will be a 24-hour closure of the intersection through March 17th. Following March 17th the intersection will close during permitted daytime hours: 7 a.m to 7 p.m. Monday through Friday and 9 a.m. to 6 p.m. Saturday. The intersection will reopen after work hours once it is safe to do so. Residential access will be maintained. For more details, see the Area 2 project updates.

In north-central Mercer Island: While crews work in the right-of-way, temporary signals or driveway assist devices move traffic through the work area safely. See the notification for details and what to expect .

On 90th PL SE: Crews continue installing the new sewer line. See the notification for details and what to expect .

On the I-90 Trail: Crews are installing pipe using an “open cut” trenching construction technique. The trail is closed from Shorewood Dr to SE 35th PL. The trail will remain closed around the clock until it has been repaved. Additionally, you may see crews in orange vests preparing for landscape restoration and tree replanting. See the notification for detours and what to expect .

On Southeast 35th Place: Crews are preparing to install a new sewer line that will run underneath streets and through the wooded area between 97th Ave SE and the cul-de-sac on SE 35th Pl. To support future operations, below-ground structures will be built in the cul-de-sac. Parking will be restricted with resident access maintained. See the notification for details and what to expect .

Construction activity in Bellevue*

At Enatai Beach Park and the Sweyolocken Pump Station: The Mercer Slough connector trail is expected to remain closed through Fall 2023. See the detour map .

Recent notifications:

Construction status

Construction status along the alignment of the North Mercer/Enatai sewer upgrade project.Click for larger view.

An excavator is fitted with a hook attachment with cables attached to a huge yellow box. Two crew members are standing beside the large yellow box.During open cut construction, construction crews use steel boxes called trench boxes to strengthen excavation walls while they install pipe deep underground. View more construction photos .

Sign up for email and text updates

Sign up for general project updates in two geographic areas:

North Mercer Island project area

Enatai project area

Click on a project area number to learn more and sign up to receive email or text updates.

Project areas: 1 | 2 | 3 | 4 | 5| 6 | 7 | 8

The construction route has been divided into 8 areas. You can sign up to receive updates for one or all of these areas.

View Construction Reference Guide.

Project description

With over four hundred miles of pipes moving wastewater to one of our award-winning treatment plants, King County WTD works hard to maintain our system. We inspect and monitor our regional system and update plans for needed upgrades.

King County WTD needs to replace sewer pipes that serve areas in North Mercer Island, the southwest portion of Bellevue near Enatai Beach, and the Town of Beaux Arts Village. This pipeline carries wastewater from the North Mercer Island Pump Station to the Sweyolocken Pump Station in Bellevue.

To learn more about what we are building, construction, and what to expect, click on the StoryMap below.

Aerial view of Lake Washington. Click Storymap: learn more about the North Mercer/Enatai Sewer Upgrade Project.


Project design began in 2016 and was completed in 2021. Construction began in early 2022 and will extend until 2025. View March 2022 project newsletter for latest schedule .


Contact us

Contact the community services leads at:
Emily Berry, 206-848-0698
Annie Pfeifer, 206-263-3203

24-hour construction hotline:

Project location

The project area spans from the North Mercer Pump Station to the Sweyolocken Pump Station (Mercer Slough)

Back to the capital projects overview map .

Lets Talk Mercer Island!

The City of Mercer Island and King County are collaborating to ensure Mercer Island residents get timely, accurate construction information. In addition to the County’s website, Let’s Talk Mercer Island will feature the project with monthly updates and will monitor for resident questions and comments. 

Related information

System planning

Local municipalities: