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Project update

May 26, 2023

Construction activity in Mercer Island*

North Mercer Way closures and detours began Monday, May 15th: Crews will work in phases on North Mercer Way between 80th Ave SE and SE 26th St for approximately 2 months. We are currently in Phase 1 of the closure. North Mercer Way will be closed at 80th and 81st Avenues Southeast. See the notification for details and detour routes .

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

On Shorewood Drive: Crews continue installing the new sewer line. See the notification for details and what to expect .

On SE 35th St: Pipe installation at North Mercer Way and SE 35th St will start as early as May 31. Residential access will be maintained. 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 SE 35th Pl: 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 are being built in the cul-de-sac. Parking is restricted with resident access maintained. See the notification for details and what to expect .

At the Mercer Island Boat Launch: As early as May 15, we will close a lane of traffic on Frontage Road for construction activities. The boat launch will stay open. Please follow traffic control measures, such as flaggers and signals, and plan for delays. See the notification for details and what to expect .

Additionally, overflow parking for the Mercer Island Boat Launch is available on weekends at City Hall. See the notification for more details .  

Construction activity in Bellevue*

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

Recent notifications:

*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 will be updated regularly based on updates given by our contractor.

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: