Mid-Spencer Island Restoration Project


The purpose of the Mid-Spencer Island Estuary Restoration Project is 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 will increase the connectivity between Steamboat Slough, Union Slough, and the other sloughs, restoring natural tidal exchange processes. Wooden logs will also be driven into the island at specific locations to encourage natural racking of additional wood pieces that would otherwise float by.

The intent of this work is to create immediate improvements to site access and habitat, enhance connectivity for the neighboring Smith Island Restoration site, and create conditions that allow for natural restoration of tidal influence and floodplain connection over the long-term. The interior of the island will then be accessible to the young salmon, restoring critically needed places to hide from predators in the cool of the shade, or to feed on the insects that accumulate on the racked up wood. 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 work being done on Mid-Spencer Island 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 is 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 will occur July to September 2019.
  • Scope: Project construction will:
    • Lower and breach the remnant dike at 16 channel locations.
    • Install 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: Public Works estimates construction will cost about $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 is 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 Estuary 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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