Salmon in the Lake Washington Watershed

Geological Formation

The present-day Lake Washington basin was shaped by glacial carving during the Vashon Glaciation between 19,000 and 16,000 years BP (before present). The Puget lobe of the Cordilleran Ice Sheet sculpted the lake's basin through a combination of erosion from the glacier itself and meltwater as it retreated. The frozen and melting water sculpted the deep, narrow glacial trough with steeply sloping sides that characterize the lake beds of Lake Washington and Lake Sammamish, and the Puget Sound basin as well. At the end of the Pleistocene era, the lake connected directly to the saltwater of the Salish Sea through the north end of the Duwamish Valley.

Examining salmon migration through the Lake Washington Watershed demonstrates a contested landscape where the temporal patterns and spatial paths of the movement of Chinook, coho, and sockeye salmon in these waterways are heavily determined now by human action. The Ballard Locks are an act of institutional control of territory, a chokepoint that determines access to the entire watershed. The temporal patterns of salmon migration have always overlapped with the months when the lakes, rivers, and streams of the watershed were warmest. Now these warmest temperatures are altering the migration patterns of the salmon into yet more alien configurations, as human forms of transportation and human technological intervention in the reproductive life cycles are required for the species to survive in the region.

Map of the Pacific Northwest showing areas flooded in the late Pleistocene by periodic breaching of the ice dam that blocked outflow of the Clark Fork River (a tributary to the Columbia River) and created Glacial Lake Missoula. (Source: Waples et al. 2008)

The genus Oncorhynchus (Pacific salmon) diverged from other salmon species by the early Miocene, 15-20 million years ago. After the end of the Pleistocene era, Oncorhynchus species re-colonized the fresh waters of present-day Washington State and British Columbia following glacial retreat. By 5,000 years before present, the salmon ecosystems in the Pacific Northwest possessed most of the characteristics they would maintain until the time of Euro-American colonization in the 19th century, with between 1,200 and 2,500 generations of salmon living in their ancestral streams.

Evolution of Pacific Salmon

Coast Salish peoples, who have inhabited the area around Lake Washington since time immemorial, had a stable and respectful relationship with salmon prior to colonization. The salmon ceremony is the only ceremonial practice among the peoples of the area that focuses on a food source animal, highlighting the salmon's cultural importance. Archaeological evidence indicates the stability of the salmon populations and its long-standing existence as a primary food source, providing up to 25% of the caloric intake of the pre-colonial populations in the Pacific Northwest. This respectful relationship continues today, as the Muckleshoot and Duwamish peoples both maintain annual First Salmon Ceremonies

Indigenous Relationships with Salmon

Warren King George, the Muckleshoot Tribe's historian, at the salmon ceremony. (Source: Spirit of the Salmon People: The Muckleshoot Story)

The Lake Washington watershed is home to several native salmonid species. The principal salmon species include Chinook (also known as King salmon), coho (silver salmon), and sockeye (red salmon). Additionally, the watershed supports steelhead trout, rainbow trout, cutthroat trout, and bull trout populations. These species have adapted to the complex ecological conditions of the watershed over thousands of years.

Chinook salmon, currently listed as threatened under the Endangered Species Act, are represented by two distinct stocks in the watershed. One population is associated with the Cedar River, which enters Lake Washington from the south, while the other is linked to the Sammamish River system at the lake's northern end. Chinook are typically the largest of the Pacific salmon species, historically reaching weights of 80-100 pounds, though such giants are increasingly rare due to habitat loss and other environmental pressures.

Sockeye salmon, which require lake environments for juvenile rearing, were likely present in Lake Washington before European settlement, but their numbers were relatively modest. Interestingly, their population increased substantially in the 1930s after local residents introduced sockeye fry from Baker Lake into the watershed's tributaries. By the 1960s, this introduced population had grown to become one of the largest sockeye runs in the lower 48 states.

Salmonid Species in the Watershed

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Three types of salmon in the Lake Washington Watershed (Source: Washington State Department of Fish and Wildlife)

Salmon populations have precipitously declined since the 1850s, as has population diversity, with estimates suggesting that over 30% of historic salmon populations in the Pacific Northwest have been extirpated. Much of this loss can be attributed to the construction of dams and other infrastructure throughout the Pacific Northwest, including the Hiram M. Chittenden Locks in Seattle (commonly known as the Ballard Locks).

The most significant disruption to salmon habitat in the Lake Washington watershed occurred with the construction of the Lake Washington Ship Canal and Ballard Locks between 1911 and 1916. This engineering project fundamentally altered the watershed's hydrology by creating an entirely new migration route for the salmon populations. Prior to this intervention, salmon had traveled southward from Lake Washington into the Black River and then to the Duwamish waterway to reach Puget Sound. The completion of the Ballard Locks forced salmon to navigate northward through Lake Union and an artificial canal system, a dramatic reversal of their ancient migration patterns.

Watershed Transformation and Salmon Decline

The watershed also harbors a unique population of kokanee salmon, a landlocked form of sockeye that completes its entire life cycle in freshwater. Historically, kokanee were a significant food source for the Snoqualmie Tribe, though their numbers have diminished considerably in recent decades.

Waterlines map contrasting the modern shorelines of Lake Washington and Seattle-area waterways with those that existed prior to 1916 (Source: The Burke Museum of Natural History)

To mitigate the impact of the Ballard Locks on migrating salmon, engineers constructed a fish ladder on the southern side of the locks. This passage allows adult salmon to bypass the locks themselves as they return from the ocean to their spawning grounds in the watershed's rivers and streams.

The original fish ladder, built alongside the locks in 1917, proved ineffective at attracting salmon, which predominantly attempted to navigate through the locks themselves. This exposed the fish to predation and injuries from boat propellers and the lock mechanisms. Recognizing these problems, the Army Corps of Engineers rebuilt the fish ladder in 1976, expanding it from 10 steps to 21 "weirs" or steps. The redesign increased the flow of attraction water with freshwater flowing swiftly out from the ladder's bottom. This freshwater flow draws salmon to the passage, as salmon detect their natal streams by scent, thus the freshwater is the key for salmon to navigate.

The Ballard Locks Fish Ladder

Salmon climbing the fish ladder at the Ballard Locks (Source: The Smithsonian)

The Ballard Locks fish ladder has an interface between saltwater and freshwater environments which is uncommon in fish ladder design. To help salmon navigate this challenging transition, engineers installed a saltwater drain system in 1975 that diverts some saltwater into the fish ladder, creating a gradual salinity gradient that mimics natural estuary conditions.

In the other tabs of this page, explore how salmon species have been impacted by government-led infrastructure efforts and anthropgenic-created climate change.

Beechie, Timothy J. "Empirical predictors of annual bed load travel distance, and implications for salmonid habitat restoration and protection." Earth Surface Processes and Landforms 26, no. 9 (2001): 1025-1034.

Cannon, Aubrey and Dongya Y. Yang. "Early storage and sedentism on the Pacific Northwest coast: Ancient DNA analysis of salmon remains from Namu, British Columbia." American Antiquity 71, no.1 (2006): 123-140.

Campbell, Sarah K. and Virginia L. Butler. "Archaeological evidence for resilience of Pacific Northwest salmon and the socioecological system over the last ~7500 years." Ecology and Society 15, no.1 (2010): 17.

Gustafson, Richard G., Robin S. Waples, James M. Myers, Laurie A. Weitkamp, Gregory J. Bryant, Orlay W. Johnson, and Jeffrey J. Hard. "Pacific salmon extinctions: quantifying lost and remaining diversity." Conservation Biology 21, no. 4 (2007): 1009-1020.

KOMO News. Spirt of the Salmon People: The Muckleshoot Story. https://www.youtube.com/watch?v=yfKooIhQki0

Harper, Barbara L. and Deward E. Walker, Jr. "Columbia River Heritage Fish Consumption Rates." Human Ecology 43 (2015): 237-245.

Waples, Robin S., George R. Pess, and Tim Beechie. "Evolutionary history of Pacific salmon in dynamic environments." Evolutionary Applications 1, no.2 (2008): 189-206.

Bibliography

Salmon Population

The Lake Washington Watershed is unique in that the adult salmon migration can be counted very accurately since every adult salmon must pass through the Fish Ladder at the Ballard Locks. Historical records indicate that the watershed once supported millions of returning salmon annually. Early settlers and indigenous accounts describe rivers so full of fish that the water appeared to boil with their movement. The contrast with today's counts, where a few thousand fish represent a day with a lot of salmon, demonstrates the cumulative impact of urban development, habitat loss, pollution, and climate change on these iconic Pacific Northwest species. The current-day migrating population of the Lake Washington Watershed are no where near those levels. In fact, the number of Chinook salmon in the Salish Sea alone have been decreasing dramatically since the 1980s.

Chinook salmon counts in the Salish Sea (Source: The Environmental Protection Agency)

The Institutional Pathway

The map below illustrates the journey these salmon must make, swimming from Puget Sound through the Ballard Locks, across the ship canal, through Lake Union, and ultimately into Lake Washington or its tributaries to spawn. This relatively narrow corridor, which were artificially created when the locks were built in 1917, now serves as the sole migration route for all salmon entering the watershed. The locks themselves present both an opportunity and a barrier: while allowing fish passage through the ladder, they've fundamentally altered the natural hydrology of the system. This change in the spatial existence of the salmon reflects the imposition of institutionally-constructed pathway for salmon, as opposed to what Jackson (1984) termed vernacular pathways, which would be dictated by the salmon themselves, returning to their natal waterways, as opposed to the anthropogenically-created fish ladder and ship canal.

The path of the Chinook, coho, and sockeye salmon through the Lake Washington Ship Canal, with numbers as represented from the 2024 counts at the Ballard Locks.

Cyclical Time

There are three primary salmonid species that migrate into the Lake Washington Watershed: Chinook (Oncorhynchus tshawytscha), sockeye (Oncorhynchus nerkai), and coho (Oncorhynchus kisutsch). Each follow their own distinct migration timing through the summer months, representing a passage of time in the Seattle summer, especially for those who live near the Locks and frequently visit. Sockeye salmon, represented by the medium teal line, dominated the early summer runs in June and July, with peak counts reaching nearly 1,600 fish in a single day in 2024. The migration of Chinook salmon (the lightest teal line) peaks in August, while coho (the darkest teal) migrate last through the Locks, with their primary migration period occuring throughout the month of September.

Time-series chart of salmon migration through the Ballard Locks in 2024. Source for date: Washington State Department of Fish and Wildlife, co-lab for creating the chart by the author.

Bibliography

Jackson, John Brinckerhoff. Discovering the Vernacular Landscape. Yale University Press, 1984.

Lackey, Robert T. "Pacific Northwest salmon: forecasting their status in 2100." Reviews in Fisheries Science 11, no. 1 (2003): 35-88.

Accessibility for Migrating Salmon

Since the establishment of Seattle in the 1850s, increasing infrastructure such as the hardening of shorelines, flood control structures, and road culverts have had devastating impacts on the ability of adult salmon migrating to rivers and streams to spawn and for young smolt to safely mature before migrating to the salt water of the Salish Sea.

For adult salmon, after their journey through the fish ladder at the Ballard Locks, there are the more than 900 county-owned fish passage barriers identified by King County's Fish Passage Restoration Program, many of which are outdated culverts beneath roads and railways. These structures too often push water through at high velocities, creating "firehose" conditions that make upstream passage impossible for migrating salmon. Over time, these high-velocity flows erode deep holes in downstream streambeds, creating waterfall effects that prevent salmon from entering culverts altogether. For species like coho and steelhead that travel further upstream to spawn and rear juveniles, these barriers have contributed to alarming population declines by effectively cutting off access to critical spawning grounds throughout the watershed.

Adult Migration Upstream

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Map of accessibility for adult salmon swimming upstream from the Ballard Locks in the Lake Washington waterway.

After the construction of the Lake Washington Ship Canal in 1916, the shoreline of Lake Washington was reduced by 7 percent, resulting in the elimination of 10 miles of natural shoreline and reduced freshwater marshland from 1,136 acres to merely 74 acres. These marshes are crucial habitat for juvenile salmon in their early development. Young Chinook salmon, who enter Lake Washington between February and mid-May seek out shallow areas with depths between 4 inches and 4 feet with slight slopes, environments where they can hide from predators and access adequate food resources.

Shoreline hardening through bulkheads, seawalls, and other artificial structures represents one of the most pervasive barriers to successful salmon migration in the watershed. Research conducted by the University of Washington has demonstrated that these modifications create cumulative, large-scale effects throughout the ecosystem, with armored beaches becoming narrower, steeper, and composed of larger sediment that is unsuitable for salmon. Studies in Lake Washington have consistently found higher populations of juvenile Chinook along unarmored shorelines compared to those with hardened edges, confirming that bulkheads and riprap directly impede migration by eliminating the shallow water refuge areas that salmon depend on during their journey.

Smolt Migration

Map of shoreline quality for juvenile salmon in the Lake Washington Watershed

The scientific evidence of impact is substantial, with meta-analyses showing seawalls supporting 23 percent lower biodiversity and 45 percent fewer organisms than natural shorelines. Even large infrastructure like the SR 520 bridge has been documented delaying migrating smolts, forcing them to alter movement patterns and increasing exposure to predators. In response to these challenges, conservation initiatives like WRIA 8's "Green Shorelines" program are promoting salmon-friendly alternatives to traditional hardened shorelines, incorporating features that provide food and shelter for juvenile salmon. These restoration efforts, while promising, face the monumental task of addressing decades of habitat degradation across one-third of Puget Sound's 2,500 miles of shoreline where natural habitat function has been lost to human infrastructure development.

Department of Ecology, State of Washington. "Watershed Restoration and Enhancement Plan WRIA 8 – Cedar Sammamish Watershed Final Draft Plan." (2020).

Hoffman, Rachel. "Nestucca/Neskowin Watersheds Culvert Prioritization and Action Plan for Fish Passage. Tillamook Estuaries Project." (2006).

King County. "Fish Passage Barrier Prioritization Summary Report 2022."

McMahon, Thomas E. "Habitat suitability index models: Coho salmon. U.S. Department of the Interior, Fish and Wildlife Service." (1983).

Rosenfeld, Jordan, Marc Porter, and Eric Parkinson. "Habitat factors affecting the abundance and distribution of juvenile cutthroat trout (Oncorhynchus clarki) and coho salmon (Oncorhynchus kisutch)." Canadian Journal of Fisheries and Aquatic Sciences 57, no. 4 (2000): 766-774.

Sobocinski, Kathryn L. The State of the Salish Sea. (2021). G. Broadhurst and N.J.K. Baloy (Contributing Eds.). Salish Sea Institute, Western Washington University.

Bibliography

The Risk of Rising Temperatures

Rising water temperatures in the Lake Washington watershed have emerged as a critical threat to the survival of Chinook, coho, and sockeye salmon populations. Pacific salmon are cold-water species that thrive in temperatures below 58°F (14.4°C), with water temperatures above 68°F (20°C) creating significant physiological stress that can be lethal. During recent summer heat waves, water temperatures in the Lake Washington Ship Canal have frequently exceeded 70°F (21.1°C), forming what scientists term a "thermal barrier" that effectively blocks salmon migration and has led to documented die-offs of returning sockeye salmon near the Ballard Locks.

The warm water impacts each salmon species differently based on their unique life histories and migration timing. Chinook salmon, already listed as threatened under the Endangered Species Act, face particular challenges as juveniles when they must navigate the shallow, increasingly warm waters of the Ship Canal during their spring migration period. Sockeye salmon, which historically created the largest sockeye run in the lower 48 states, are especially vulnerable because they spend a full year rearing in Lake Washington, where they face extended exposure to warming temperatures. Coho salmon experience the thermal challenges during their fall spawning migrations, when the accumulated heat stress from summer warming can weaken their immune systems and increase susceptibility to diseases and parasites.

Fluctuations in temperature throughout the months of June, July, August, and September 2024. These are the months when salmon are migrating into the Lake Washington Watershed. Source (Temperature data from King County, Washington Open Data. Extrapolation for daily temperatures done by author by use of a Python script using Scipy)

Anthropogenic-driven climate change has resulted in even stranger transportation for salmon than hardened shorelines and narrow ship canals. In response to lethal temperature conditions, fisheries managers have implemented emergency interventions that often involve physically transporting salmon past thermal barriers. During particularly severe heat events, such as those in early July 2021, state and tribal fisheries crews use specialized trucks with oxygenated holding tanks to capture salmon trapped below thermal barriers and transport them to cooler upstream waters where they can continue their migration or directly to hatcheries on the Cedar River or Issaquah Creek. This labor-intensive process requires careful handling to minimize additional stress on fish already compromised by high temperatures and represents an emergency measure rather than a sustainable long-term solution to the watershed's rising temperatures.

Ever Stranger Paths for Salmon

Left: A dipnet scoops up sockeye salmon in the fish ladder as seen from the viewing room at the Ballard Locks in Seattle in July 2023. Muckleshoot fisheries staff use dipnets to pull fish and transport them to a nearby hatchery. Right: Muckleshoot Tribe workers hand sockeye caught at the Ballard Locks to Department of Fish and Wildlife staff at a nearby dock in the Lake Washington Ship Canal. Source: The Seattle Times.

Bibliography

Breda, Isabella. "Inside the effort to truck sockeye salmon past Lake Washington." The Seattle Times. 30th November 2023.