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Sammamish River Capital Investment Strategy

Project overview

The Sammamish River runs 13 miles between Lake Sammamish and Lake Washington. The river is a federal flood project called the Sammamish River Improvement Project (Flood Project). King County, as a service provider to the King County Flood Control District, maintains the Flood Project’s function. Maintenance is guided by the 1964 Operations & Maintenance Manual (O&M Manual).

Land use has changed along the river since 1964. Regulatory requirements for river maintenance have become more complex. Projects that impact the river need special permission from both King County and the U.S. Army Corps of Engineers. Permits are also needed from other federal, state, and local agencies.

The Corps of Engineers is partnering with the County on this CIS. At the same time, the Corps will update the O&M Manual to address contemporary regulations. The CIS and O&M Manual update will have separate public processes.


The Flood Project was designed to protect farmland in the spring and vacation homes on Lake Sammamish. The constructed channel is straighter and deeper than it was in the past. Remnants of the historic winding channel remain visible in aerial photography.

The O&M Manual outlines project performance standards and maintenance requirements. Land use and environmental laws have changed since the time of project construction. Many of the requirements of the O&M Manual are no longer practical, because they impair water quality and damage migratory habitat for Chinook salmon that are protected by tribal treaty rights, Washington State’s Priority Habitat and Species Program, and the Endangered Species Act.

Did you know?

The Sammamish River was once part of an ancient lake connecting Lake Washington and Lake Sammamish. For an interactive Sammamish River history experience visit the Sammamish River StoryMap.

View the Sammamish River StoryMap

Project goals

The goals of the Sammamish River Capital Investment Strategy (CIS) are to:

  1. Develop a capital investment strategy (CIS) and maintenance plan that meets the flood risk reduction, fish habitat, and navigation requirements of the O&M Manual. Use a watershed approach to include Lake Sammamish, Bear Creek, Issaquah Creek, and Willowmoor Floodplain Restoration Project considerations. Ensure the CIS reflects current jurisdictional boundaries and regulatory requirements.
  2. Work with partners to determine a strategy for implementing the 2002 U.S. Army Corps of Engineers Sammamish River Corridor Action Plan. The 2002 plan was developed to address habitat problems related to the original project design and construction.
  3. Support a Corps of Engineers update to the O&M Manual that will support implementation of these projects.

Capital investment strategy schedule

CIS project planning phase
Plan development phase
2022 to 2024
District review and approval phase
Project implementation phase
2025 to 2045

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