Chinook salmon return to historical habitat following removal of four US dams
The Klamath River in the U.S. was heavily dammed over the 20th century, blocking spawning Chinook salmon. As a result, the population of salmon that spawned in the river, which runs through Southern Oregon and Northern…
Source: Mongabay · October 13, 2026 at 11:32 AM · AI-assisted report
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NEW YORK, 13 OCTOBER 2026 —
Chinook salmon have made a rapid return to their historical habitat in the Klamath River following the removal of four large dams in the United States, according to the findings of a recent scientific study.
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The river, which flows through Southern Oregon and Northern California, had been heavily dammed over the course of the 20th century, a process that blocked spawning Chinook salmon and caused their population in the waterway to decline by roughly 90%.
The restoration initiative reached a major milestone in 2024 when four dams were removed from the Klamath River. This major engineering and environmental intervention allowed Chinook salmon, known scientifically as Oncorhynchus tshawytscha, to recolonize habitat that had been completely unavailable to them for approximately a century.
Shortly after the dams were taken down, a total of 7,742 Chinook salmon were recorded migrating up the Klamath River past the locations where the former dams once stood. The momentum of the return accelerated notably the following year, when the count jumped to more than 13,000 fish in 2025.
According to the study, the migrating fish successfully expanded into 345 kilometers, equivalent to 214 miles, of formerly blocked river, effectively recolonizing 88% of their known historical habitat.
Damon Goodman, the first author of the study, stated in an email to Mongabay that researchers had indeed expected the Chinook salmon to return to the river eventually, but they had initially remained uncertain about how long the recovery process would take. What surprised the research team was the sheer speed and scale of the fish response.
Goodman remarked that it felt like they were running to keep up with the fish, noting that these animals successfully navigated challenging rapids, engineered fishways, and a large lake to reach habitats that had been inaccessible for more than a century.
To track this migration, Goodman and his research colleagues employed a specialized underwater sonar camera that utilizes sound waves instead of traditional light to produce moving images of fish swimming through the river channel. Goodman explained that this equipment functions essentially as an underwater video camera capable of seeing clearly through muddy water and operating even in complete darkness.
The researchers installed this advanced camera near the former Iron Gate Dam site and maintained continuous monitoring of the fish throughout the entire fall migration period. Through this technology, the team was able to measure individual fish and successfully distinguish Chinook salmon from other fish species, allowing them to accurately estimate the total number of salmon passing through the monitoring site.
Goodman noted that this technology proved particularly valuable because the Klamath River remained extremely turbid following the dam removal process, which made standard underwater video monitoring entirely impractical. He emphasized that the sonar system allowed the research team to document the return of thousands of salmon that otherwise would have been extremely difficult to observe using conventional methods.
Despite the positive early results, Goodman expressed a cautious outlook regarding the long-term prospects of the species, stating that while the Klamath Chinook salmon could experience a substantial recovery, they are not out of the woods yet. He explained that the speed of recolonization demonstrates that these fish retain a remarkable ability to find and utilize newly accessible habitat.
However, Goodman cautioned that returning to historical population levels will require successful reproduction over multiple generations, along with ongoing improvements in overall habitat conditions, water quality, and fish passage throughout the entire river basin. He concluded that while dam removal was an enormous step forward, it does not eliminate all the challenges currently facing the salmon population.
External scientific observers have echoed the assessment of the study's authors regarding the velocity of the ecological response. Scott Hinch, a salmon ecologist at the University of British Columbia who was not involved in the research, told The New York Times that the speed of the salmon recovery is remarkable. Hinch observed that everything has to fall into place to make an environmental restoration of this magnitude possible.
Related: Damon Goodman