Each year, the Washington Chapter of the American Water Resources Association (AWRA-WA) hosts a conference dedicated to the myriad ways in which water shapes the lives, economy, and environment in Washington state and beyond. This year, AWRA-WA’s annual conference turns its focus to water quality in Washington, how water quality affects the designated and beneficial uses of water, and what Washington is doing to address those concerns. Thomas Mathis, P.H., a senior consultant at DSI LLC, wrote this an article for the annual conference. The article addresses the innovative solutions being used to address temperature concerns for salmon populations in the Lake Washington Ship Canal.
Washington’s waterways are facing unprecedented challenges, particularly in the Lake Washington Ship Canal (LWSC), where elevated water temperatures are posing a serious threat to salmon populations. As the climate continues to warm, the canal—a vital migratory route for salmon in the Lake Washington, Cedar, and Sammamish Watershed (WRIA 8)—has seen increasingly harmful water temperatures. These temperature spikes are especially dangerous for adult salmon, impacting their migration, spawning success, and overall survival.
A collaborative partnership, led by Long Live the Kings (LLTK), has come together to address these urgent issues. Working alongside the WRIA 8 Salmon Recovery Council, the team includes Jacobs Engineering, which has conducted an in-depth feasibility study, and DSI LLC, which has provided advanced hydrodynamic modeling to guide the project’s development. Together, they are pursuing innovative solutions to create cooler water pathways in the LWSC that will improve conditions for salmon as they navigate these increasingly inhospitable waters.
Temperature is the most pressing issue in the Lake Washington Ship Canal. Salmon are cold-water species, and when water temperatures exceed 19°C, adult salmon face lethal and sublethal effects that can drastically reduce their chances of survival. In recent years, the canal has experienced temperatures well above this threshold during key migration periods, placing tremendous stress on salmon populations and contributing to declining numbers.
The collaborative project led by LLTK focuses on reducing water temperatures to create a more suitable environment for salmon. This involves exploring innovative methods of introducing cooler water into the canal to create thermal refuges—areas where salmon can find respite from the warmer surrounding waters. By reducing the number of days when temperatures exceed critical thresholds, the project aims to support the continued survival of salmon populations in the watershed.
Central to this project is the use of hydrodynamic modeling, provided by DSI LLC, which allows the team to simulate various scenarios for introducing cooler water into the LWSC. This modeling is crucial in determining the best locations and methods for cooling the water. DSI’s simulations have shown that drawing cooler water from the hypolimnion—the deep, colder layers of Lake Washington—and channeling it into the LWSC could create a consistent pathway of cooler water, benefiting migrating salmon.
The models developed by DSI have provided valuable insights into how water moves through the canal and how different cooling strategies might interact with the canal's existing hydrodynamics. For example, modeling has helped identify where and how much cool water can be introduced to have the greatest impact on water temperatures while avoiding unintended consequences such as disrupting salmon migration patterns.
In addition to modeling, Jacobs Engineering has been instrumental in evaluating the feasibility of various cooling strategies. Their work has examined the potential for large-scale engineered solutions, such as pumping cold water from Lake Washington’s hypolimnion into the LWSC. This approach could provide a continuous flow of cooler water, creating a temperature buffer that would help adult salmon during their migration through the canal. Jacobs’ feasibility study has also considered the scale of infrastructure needed, the associated costs, and potential environmental impacts.
While cooling the entire canal is not feasible, the project is focused on creating targeted areas of cooler water that would offer salmon a safe passage through the most critical parts of the canal. This project is an ambitious, large-scale effort, but it has the potential to generate significant benefits, not only for the survival of salmon but also for the overall health of the watershed.
Adult salmon are a keystone species in the Pacific Northwest, playing a vital role in the region’s ecology, economy, and culture. Their survival is crucial, not only for the species itself but also for the many communities that rely on them. Tribal nations, in particular, hold treaty rights to harvest salmon, and any decline in salmon populations threatens both their cultural heritage and livelihood.
This project recognizes the critical importance of ensuring that adult salmon can successfully navigate the LWSC. By focusing on temperature management, the partnership aims to protect the salmon during one of the most vulnerable stages of their life cycle. Lowering water temperatures will give adult salmon a better chance to survive their journey, spawn successfully, and maintain the population’s future viability.
The effort to improve water quality in the Lake Washington Ship Canal is a testament to the power of collaboration. Led by Long Live the Kings, with crucial contributions from Jacobs and DSI LLC, this project brings together expertise from environmental organizations, tribal communities, government agencies, and the private sector. Together, they are developing a multifaceted approach to address the challenges posed by rising temperatures, ensuring a future where salmon populations can thrive in the face of climate change.
As this project progresses, continued modeling, testing, and collaboration will be essential. The partnership’s commitment to finding science-based solutions offers hope that, with the right interventions, Washington’s salmon populations will continue to swim these waters for generations to come.
