Sammamish Plateau Diversion

Project update

This section includes project updates. For more details, read our latest project email. You can view previous project updates below. Sign up for our listserv to stay up to date.

Fall 2026

Come talk to us at Issaquah Salmon Days!

We will be at the Issaquah Salmon Days in early October. Stop by our booth to learn about:

• Our projects in the area, including the Sammamish Plateau Diversion and the Coal Creek Sewer Upgrade projects
• King County's regional wastewater system
• How you can protect local waterways

• Date: Saturday, October 3, and Sunday, October 4
• Time: 10 a.m. to 6 p.m.
• Location: Issaquah Salmon Hatchery, 125 West Sunset Way
• Event website: salmondays.org

A community member and King County WTD representative talking at Issaquah Salmon Days 2025.

Summer events recap

The project team was in the community all summer! We shared project information, answered questions, and gathered feedback. We enjoyed meeting nearly 200 interested community members at the GoGreen Movie Night in Marymoor Park on July 22 and the Sammamish Farmers Market on August 19. We heard comments and questions about:

• How the Sammamish Plateau Diversion project may impact neighbors and people in the area
• Traffic impacts
• The project schedule
• Ways to stay informed about project updates
• How to protect our regional wastewater system

We provided giveaways and project materials for people to take home and learn more. These materials were offered in English, Spanish, Traditional Chinese, Simplified Chinese, Japanese, Korean, and Russian.

The project is early in design. There are still a lot of details to figure out. The project team will do more field work to understand where and how to build the new wastewater pipes.

Now is a great time to learn about the project, share your feedback, and ask questions. We hope to see you at the Issaquah Salmon Days on October 3 and 4.

A King County WTD representative and community member discussed the project at the Sammamish Farmers Market in August 2026.

Learn about the project: Sammamish Plateau Diversion - King County, Washington

Clogged but not forgotten

What’s the harm in flushing that one disposable wipe? Imagine thousands of your neighbors doing the same thing. They quickly become a nightmare for our wastewater operators, who have to unclog the pumps to keep wastewater moving through our regional system.

Wipes don’t break down like toilet paper. They can also cause problems in your home’s side sewer or septic system!

Inside the pipes, disposable wipes, hygiene products, paper towels, and other trash combine into “rag balls.” These rag balls clog pipes and put our health and Puget Sound at risk.

A “rag ball” clog made of “flushable” wipes and trash. Do not flush anything besides toilet paper and what comes out of your body. The toilet is not a trash can!

Find out how King County operators are tackling the issue and how you can help: Clogged, not forgotten: The hidden reality when you flush wipes