SR 6 - Two Tributaries to Chehalis River Fish Passage

Project news

In summer 2020, contractor crews working for the Washington State Department of Transportation will begin the work to remove and replace two culverts leading to the Chehalis River located underneath SR 6, near Twin Oaks Road, (between mileposts: 46.32 to 46.59) in Lewis County. 

Needs & benefits

Constructed in 1971, these two culverts, which are generally large pipes beneath roadways, are in need of replacement in order to meet a federal court injunction, issued in March 2013. This injunction requires the state to increase the effort for removing state-owned culverts that block habitats for salmon and steelhead by 2030. Replacing these two fish barriers are a part of this effort.

Why does WSDOT have barrier culverts?

Most of the culverts were installed decades before scientists fully understood the needs of fish. WSDOT met all requirements for culvert installation and sizing at the time they were constructed. In addition, a culvert that was fish passable at the time of installation might have become a barrier over time due to changes in the landscape resulting from development, logging and fire. 

The end result

A single removed barrier can deliver impressive benefits, improving fish access for miles both upstream and downstream. Once construction is complete, the new fish-friendly structure will be much larger and should be more resilient to changes in the landscape and provide for fish passage long into the future - giving fish better access the habitat they need. This is an important component of protecting and restoring fish populations, which can in turn have multiple benefits - including for commercial and recreational fishing industries. To learn more about our fish passage improvements, visit our Improving Fish Passage webpage. 

  • Protects Environment: Improving fish passage by opening up the stream creates an additional fish habitat.
  • Improves Safety: Replacing the culverts with a concrete bridge span lessens erosion around roads by providing better drainage.
  • Reduce Costly Repairs: Replacing the culverts with a concrete bridge span will reduce the cost of emergency maintenance repairs.

What to expect during construction

A shoe-fly detour or bypass will be constructed to divert traffic around the work zone. This will keep travelers moving while construction is on going. Additionally, beginning summer 2020 the posted speed limit for this detour will be 25 mph. This speed limit reduction will remain in place until construction is completed, in fall 2021. While no major delays are scheduled, there will be around-the-clock flagging, which permits delays up to 20 minutes for approximately 48 hours, however these delays are not scheduled until early 2021.     


  • Spring 2020 - Project was awarded to Scarsella Bros. Inc. on May 19, 2020
  • Summer 2020 - Construction scheduled to begin
  • Spring 2021: Bridge girder placement work begins
  • Fall 2021 - Project scheduled for completion 


The estimated cost of this project is approximately $8.9 million dollars, and is a combination of both state and federal funding. 


Financial Data for PIN 400621J
Funding Source Amount ($ in thousands)
2003 Gas Tax (Nickel Funding) $0
2005 Gas Tax (TPA) $0
Pre-Existing Funds (PEF) $10,560
CWA $320
Total $10,880


Colin Newell - Project Engineer

Celeste Dimichina - WSDOT Communications

State Route 6 - Two Tributaries to Chehalis River - Fish Passage project location