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 pinpoint the cause of high steelhead mortality and to gauge the bridge’s effect on water quality. As the assessment progresses, the team will work with managers to develop, test, refine, and carry out solutions to address adverse impacts of the bridge without undermining the bridge’s role as a major transportation fixture.

The Problem

The Hood Canal Bridge carries State Route 104 across the Canal’s northern outlet, connecting the Olympic and Kitsap Peninsulas. A floating bridge, its pontoons span 83% of the width of Hood Canal and extend 15 feet underwater.

Recent studies via our Hood Canal Steelhead Project show 65% of juvenile, ESA-listed steelhead that reach the Hood Canal Bridge do not make it north to the Strait of Juan de Fuca, with strong evidence that the bridge is acting as migration barrier, driving this mortality. This level of mortality is alarming, and observations indicate that juvenile Chinook and summer chum, again listed as threatened under the Endangered Species Act, may also be affected.

Moreover, computer modeling suggests the bridge’s pontoons may reduce circulation in and out of the Canal by 12%. While that number seems small, it could be enough to significantly impact the Hood Canal ecosystem: increasing temperatures, lowering dissolved oxygen levels, and exacerbating the effects of ocean acidification and climate change.

This dual threat to steelhead, salmon and their local marine ecosystem may severely limit the effectiveness of millions of dollars already spent in Hood Canal by LLTK and other groups to prevent extinction*, restore habitat, and reduce water pollution. Without addressing the impacts of the bridge, landowners, fishermen, shellfish farmers, and the cities and counties they work within may continue to pay the price.

Our Solution

Long Live the Kings and our partners have completed an independently reviewed assessment plan that takes a stepwise approach to efficiently pinpoint the causes of the problems and implement solutions. Over the next 2 years (through early 2019), we will identify: where and how the bridge pontoons slow steelhead migration, heighten fish densities, and increase the susceptibility of salmon and steelhead to predation; whether light, shade, and noise impacts from the bridge affect fish and/or predator behavior; and whether structural voids in the bridge may aggregate plankton, attracting salmon and increasing their susceptibility to predation. We will also quantify how the bridge affects circulation and water quality throughout Hood Canal, including dissolved oxygen, temperature, acidity, and nutrients. With this information, the assessment will test and ultimately guide the implementation of solutions.

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

Project Manager

206.382.9555, x30 lhall@lltk.org