Lower Issaquah Creek Restoration at Lake Sammamish State Park

The Mountains to Sound Greenway Trust and the Washington State Parks and Recreation Commission are partnering to study in-stream habitat and natural process improvements along the lower 6,000 feet of Issaquah Creek that flows through Lake Sammamish State Park. With 1.3 million annual visitors to the State Park, this project will be highly visible with tremendous community outreach and education opportunity. When completed (construction is currently planned for summer of 2023), along with other efforts underway by State Parks and the City of Issaquah, it will finish nearly all restoration that is proposed in the lower reach of Issaquah Creek in the 2005 Chinook Salmon Conservation Plan (WRIA 8, 2005) and the 2017 update to the Plan (WRIA 8, 2017).

After a decade plus of incremental riparian restoration projects in the State Park, adding three-to-five acres annually along the banks of Issaquah Creek, partners from the WRIA 8 Technical Committee encouraged the Greenway Trust to pursue a more comprehensive ecological in-stream restoration effort. Specifically, a restoration effort that would leverage the slowly maturing native forest (now 50+ acres of riparian buffer planted in the State Park) by completing an analysis of instream habitat conditions, evaluating opportunities for increased relict-channel and floodplain connections, and placement of large woody material (LWM) features to improve conditions for juvenile Chinook and other salmonid species. This project represents the assessment of this effort to date, and includes most of the final remaining A-, B-, and C-level projects from the 2005 Lake Sammamish State Park Wetland, Stream, and Lakeshore Restoration Plan.

Conceptual Design Report

The Lower Issaquah Creek Restoration at Lake Sammamish State Park Conceptual Design Report was completed in December of 2018. The report describes existing channel conditions, breaking down the project into four reaches defined by geomorphology and current habitat features. The report also outlines project objectives and presents two alternatives for in-stream restoration. The two alternatives were  shared with project partners and stakeholders, with Alternative 2 being the unanimous preferred alternative. After the selection of Alternative 2, further outreach was conducted to refine the Conceptual Design which is reflected in the Updated Conceptual Design Drawings.

Preliminary Design Report

The Lower Issaquah Creek Restoration at Lake Sammamish State Park Preliminary Design Report was completed in September of 2020. Following the Recreation and Conservation Office (RCO) Guidelines for Design and Restoration Project Deliverables, the report documents the following:

  1. Project history and background
  2. Project objectives for all four reaches
  3. Descriptions of infrastructure
  4. LWM Inventory
  5. Hydraulic modeling
  6. Channel migration zone analysis
  7. Outreach and engagement with interest groups
  8. Preliminary cost estimates

Preliminary Report

Preliminary Report with Appendices

Full Appendices

Project Construction

Phase 1 (Reach 2 and Reach 3) project construction is currently planned for the summer of 2023.

Project Funding

Funding for this effort comes through a King County Flood Control District Cooperative Watershed Management grant via the Lake Washington/Cedar/Sammamish Watershed (WRIA 8), the Washington State Salmon Recovery Funding Board (SRFB) through WRIA 8, the Washington State Recreation and Conservation Office (RCO), and a grant from The Boeing Company. The Greenway Trust has contracted with Northwest Hydraulic Consultants (NHC), and The Watershed Company to evaluate alternatives and develop a preliminary design to enhance this stretch of Issaquah Creek.