Hood Canal Bridge Ecosystem Impact Assessment

Steelhead are dying at the Hood Canal Bridge. Salmon may also be affected. How can we fix this?

Project Overview

Long Live the Kings, in partnership with the Hood Canal Coordinating Council, Tribes, and state and federal agencies, is working to address high steelhead mortality at this floating bridge. Phase 1 has concluded, and the report summary and full report are available below. Phase 2 is underway, and engineers are designing guidance structures to reduce steelhead mortality. A total of $3.6 million was secured through a legislative appropriation for developing and testing the guidance structures, which will be deployed and assessed in the spring of 2023. We hope to secure additional funding to construct a second structure, conduct two more years of testing, further research into salmon mortality, and improve and redeploy the guidance structures. Long-term solutions will likely include replacing or significantly retrofitting the bridge.

The Problem

Vital elements of Hood Canal’s natural ecosystem are at risk. Wild salmon in Hood Canal — including Chinook, chum, and steelhead — are listed as threatened under the Endangered Species Act.

The Hood Canal Bridge spans the northern outlet of Hood Canal, connecting the Olympic and Kitsap peninsulas. As a floating bridge, its pontoons span 83% of the width of Hood Canal and extend 15 feet down from the water surface.

Tracking data from Phase 1 results indicate that up to 50% of juvenile steelhead that make it to the bridge do not survive past it. Migrating steelhead are generally swimming near the surface, where the bridge pontoons create an obstruction, increasing fish densities and making juvenile steelhead more vulnerable to predators. These fish can take a day or two to find their way past the bridge, when normally they take just 5 to 7 hours to travel a similar distance through open reaches of the canal. Light, shade, and noise from the bridge may lend an advantage to predators but do not appear to directly contribute to fish mortality. Furthermore, certain portions of the bridge appear to collect plankton, encouraging hungry Chinook, chum and forage fish to linger at the bridge, which could increase their susceptibility to predation.

Furthermore, water quality modeling shows that the bridge impacts temperature, salinity, and currents down to ~65 feet below the water surface and up to 1.25 to 3 miles away from the bridge. This dual threat to fish and their ecosystem may be limiting the effectiveness of millions of dollars already spent recovering steelhead, salmon, and their habitat in Hood Canal.

Our Solution

Long Live the Kings and our partners are executing an independently reviewed assessment plan that takes a stepwise approach to efficiently pinpoint the causes of the problems and implement solutions. Over two years of research (2017 and 2018), the team tagged and tracked nearly 500 juvenile steelhead and collected data on light, noise, fish density, predators, currents, temperatures, and hundreds of other observations. The synthesis of these data has given us valuable insight into how the bridge is exacerbating fish mortality.

Two panel diagram: first panel is titled Observed Fish Behavior, showing salmon swimming into a 90 degree corner at the Hood Canal bridge with a harbor seal nearby. Second Panel is titled "with corner fish guidance structure" and shows a triangular wedge inserted into the corner, with fish following a smoother path around and under the bridge reading "safe passage."
This diagram shows the sharp corners on the bridge’s floating pylons, where migrating juvenile steelhead can become stuck and easy targets for predators. The second panel shows how a fish guidance structure may help redirect the fish more quickly around and under the bridge.

Based on our research, engineers and fish passage experts are working with the team to develop short-term mitigation strategies to help fish pass the bridge more quickly, and deter predators from foraging near the bridge. In 2022, LLTK awarded a contract to Global Diving and Salvage to build the first fish guidance structure for the Hood Canal Bridge. Engineers from Kleinschmidt Associates and Art Anderson Associates designed this structure to help guide fish around the bridge more quickly. Global and their partners at Pacific Netting Products will be constructing the high-density polyethylene (HDPE) floating structure over the fall and winter. In Spring 2023, our partners at NOAA and the Port Gamble S’Klallam Tribe will be monitoring juvenile steelhead and salmon migrating around the bridge, during deployments of the guidance structure. The structure will be tested every other week for six weeks, with the off weeks used as experimental “controls” to see what the survival and fish passage timing is like without the structure in place. We hope to see data confirming that the structure helps more fish make it safely past the bridge while we continue to work on long-term solutions, including fundamental changes to the bridge’s design.

Engineering schematic of a triangular fillet measuring approximately 60' per side (85' diagonal) and 21.5 feet tall.
Design schematic showing the structure of the fish guidance structure, called a “fillet,” to be tested at the Hood Canal Bridge in 2023.

Project Updates

View the Phase 1 report summary here. 

View the Phase 1 assessment report here.

View NOAA’s scientific paper on Hood Canal steelhead survival here. 

View the full assessment plan here.

View our Hood Canal Bridge handout here.

*See our work to boost the numbers of steelhead and summer chum at the brink of extinction.

Project Impact

7

partnering agencies

$2.4m

invested to-date

4

steelhead stocks affected

Project Partners

< Swipe left to see more

Project Contact

Lucas Hall

Associate Director for Government Relations and Special Projects (he/him/his)

206.382.9555, x30 lhall@lltk.org