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 are working to address high steelhead mortality at this floating bridge. Phase 1 data collection is completed and the report will be available in early 2020. While the report is being finalized, the team is planning for Phase 2 of the assessment where we will pilot short term mitigation strategies. Long-term solutions that do not undermine the bridge as a transportation corridor are also being considered.

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 into the upper water layer.

Tracking data from the preliminary Phase 1 results indicate that up to 50% of juvenile steelhead that make it to the bridge do not survive past it. Bridge pontoons create an obstruction, increasing fish densities and making juvenile steelhead more vulnerable to predators near the bridge. 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 aggregate plankton, incentivizing 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 ~20 m below the water surface and up to 2-5 km 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 has 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 this data is giving us valuable insight into how the bridge is exacerbating fish mortality.

Based on our research, engineers and fish passage experts will work with the team to develop short-term mitigation strategies that will expedite fish passage and deter predators from foraging near the bridge. At the same time, we are working to explore long-term options that may include fundamental changes to the bridge’s design.


2020 Project Update from LLTK Senior Project Manager – Iris Kemp!

View the full assessment plan here.

View the Hood Canal Bridge handout here.

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

Project Impact


partnering agencies


invested to-date


steelhead stocks affected

Project Partners

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Project Contact

Lucas Hall

Senior Project Manager

206.382.9555, x30 lhall@lltk.org