High water temperature is a deadly threat to salmon in the highly urbanized Lake Washington Ship Canal. How can we solve this unique challenge and support the salmon’s survival?
Each summer, sockeye, coho, and threatened Chinook salmon battle worsening conditions on their journey through the heart of Seattle. Hot water temperatures in Lake Washington Ship Canal can be lethal to salmon and only a fraction of salmon reach their spawning grounds in the Cedar and Sammamish Rivers. These Pacific Northwest icons are on a path to extinction in and it’s happening in Seattle’s backyard.
To save these salmon we need to understand the deadly challenges they’re facing, come together, and act before it’s too late.
Lake Washington sockeye salmon, once the largest sockeye run in the Lower 48, have not returned at numbers needed to support a fishery since 2006 and are on the verge of collapse. Chinook salmon are listed as “Threatened” under the Endangered Species Act. Over $125 million has been spent restoring fish access and habitat upstream in the basin of the Ship Canal. All of this may be in vain if water temperature in the Ship Canal continues to increase.
High water temperatures have been a problem in the Lake Washington Ship Canal for more than two decades, and the problem is only getting worse. During the June 2021 heat wave, when Seattle reached a record-breaking 108°F, dead sockeye were found around the Ballard Locks fish ladder.
The 2021 heat wave is not an isolated incident. Climate change is causing increasing average annual temperatures and extreme weather events. Extreme temperatures have a generational ripple effect in struggling salmon populations. Even if they can survive to reach their spawning grounds, fish weakened from high temperatures may be less successful in reproducing. These issues will continue to worsen as the impacts of climate change persist.
The warmer water also provides favorable conditions for invasive fish that eat young salmon. There are a few deeper locations in the Ship Canal with colder water, but they often don’t have enough oxygen for the fish to survive. At the Ballard Locks, migrating salmon must transition between cold saltwater and hot freshwater within a few hundred yards. These changes have major impacts on juvenile and adult salmon, including delayed or blocked migration, higher mortality due to increased susceptibility to diseases, fungi, and parasites, and even death.
Addressing issues of water quality is an important step to save threatened salmon runs and to bring Tribal and recreational salmon fishing back to the watershed. Without addressing the high temperatures and low dissolved oxygen in the Ship Canal, long-term salmon recovery in the Cedar and Sammamish watersheds will be nearly impossible.
The Lake Washington Ship Canal is a unique challenge for salmon passage: a human-made environment in the most populous watershed in Washington State. Typical restoration actions, like planting trees for shade, aren’t enough, and they aren’t practical solutions in this area. To save these beloved salmon runs, we will need innovative ideas and community-wide investment to bring cooler waters to the Ship Canal.
Long Live the Kings and the Lake Washington/Cedar/Sammamish Watershed (WRIA 8) Salmon Recovery Council are partnering to build off the work that many are doing to address this urgent issue. In 2020, we convened a team of government and community partners to review the science and evaluate possible solutions to help salmon pass safely through the Ship Canal. The first report from that effort was released in early 2023. It recommends studying the feasibility of alternatives to pump cooler water into the Ship Canal.
The goal of these solutions is to create a continuous pathway or connected pockets of water within the Ship Canal where water temperatures and dissolved oxygen levels are within the healthy range for salmon, allowing them to migrate freely.
At the same time, urgent short-term solutions are also necessary to keep the salmon runs from collapsing while a long-term fix is in progress. These actions could include changes to operations and redesigning fish passage at the Ballard Locks, where adult salmon face the difficult transition from cool saltwater to warm, low-oxygen freshwater in the Ship Canal.
As Seattle’s summers get warmer, our experts agree that we need to pursue multiple strategies to prevent the extinction of these salmon runs, now and for generations to come.
Phase 1 of the work to address warm temperatures in the Ship Canal, completed in July 2022, focused on reviewing the science and aligning partners around a mutual goal, and prioritizing promising solutions for further analysis.
In Phase 2, which began in 2023, the group is completing an initial feasibility analysis, pursuing water temperature modeling, developing strategies to implement solutions, and supporting ongoing work.
Phase 3 will put the solutions into action.
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