Mid-Spencer Island Restoration Project


The purpose of the Mid-Spencer Island Restoration Project was to enlarge existing dike breaches and construct new breaches on Mid-Spencer Island as part of restoration efforts in the Snohomish River estuary. This construction increased the connectivity between Steamboat Slough, Union Slough, and the other sloughs, restoring natural tidal exchange processes. Wooden logs were placed at specific locations to encourage natural racking of additional wood pieces that would otherwise float by.

This project created immediate improvements to site access and habitat by enhancing connectivity for the neighboring Smith Island Restoration site and creating conditions that allow for the natural restoration of tidal influence and floodplain connection over the long-term. The interior of the island is now accessible to young salmon, providing critical habitat and food sources. Without these areas of refuge, the river currents are too fast, too warm, and too barren for juvenile fish to feed and hide.


The project site is owned and managed by Snohomish County for conservation purposes. The former estuary habitat area was diked and farmed a century ago. Farming was abandoned in the late 1960s. Historic dike construction, timber harvest, and other development eliminated tidal channel networks and distributary sloughs, significantly reducing Snohomish River Estuary wetland habitats.  

The Mid-Spencer Island Restoration Project is part of a larger regional effort that includes the Smith Island Restoration project (Snohomish County), the City of Everett’s Union Slough project, the Port of Everett’s Blue Heron project, and the Tulalip Tribe’s Qwuloolt Estuary project.

​Project Facts

  • Size and location: The project site includes 74 acres in the Snohomish River estuary on Spencer Island, surrounded by Steamboat Slough and Union Slough, and adjacent to the Smith Island project in Everett, WA.
  • Timeframe: Construction took three months to complete and finished in October 2019.
  • Scope: Project construction successfully:
    • Lowered and breached the remnant dike at 16 channel locations.
    • Installed vertical wood logs, placed into rows, to collect and hold driftwood and sediment. This will help establish native vegetation succession and food web recovery.
  • Costs: Construction cost approximately $1.3 million.
  • Funding Sources: 
    • Snohomish County Public Works Surface Water Management (SWM)
    • National Oceanic and Atmospheric Administration (NOAA) Coastal Ecosystem Resiliency Grants Program
    • Washington Recreation and Conservation Office (RCO) Salmon Recovery Funding Board (SRFB) Salmon State funds and Puget Sound Acquisition and Restoration (PSAR) program


This project was identified in the 2005 Snohomish Basin Salmon Recovery Plan as a primary action to help restore the Snohomish River basin Chinook salmon, helping to meet 10-year estuary restoration goals. The Mid-Spencer project is adjacent to the Smith Island project aligning reconnected tidal channels on both sides of Union Slough. The Steamboat Slough connections further increase juvenile salmon access between the estuary sloughs and the two projects.

Chinook salmon are considered a threatened species under the Endangered Species Act. By federal law, agencies are obligated to increase Chinook salmon in Puget Sound, and this project significantly expands available salmon habitat for juvenile salmon on their way to the ocean. Chinook salmon are also the primary food source for the Endangered Southern Resident Killer Whale.

Restoration efforts in the Snohomish River basin are vitally important for salmon recovery in Puget Sound. At 1,856 square miles, the Snohomish River basin is the second-largest watershed -- behind the Skagit River basin -- draining to Puget Sound. The Snohomish River basin includes the Skykomish and Snoqualmie rivers, which join the Snohomish River and numerous smaller tributaries that total 2,718 miles in length. 

The Mid-Spencer Island Restoration Project demonstrates SWM's commitment to its mission of protecting and enhancing our water resources for future generations by restoring fish habitats.

Special Thank You to Our Funders!

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