Chinook salmon have rapidly recolonised historical habitat in the Klamath River following the removal of four dams in 2024. Flowing through southern Oregon and northern California, the river was extensively dammed during the twentieth century, obstructing access to spawning grounds. Its spawning salmon population subsequently declined by roughly 90%. According to a recent study, 7,742 Chinook migrated upstream beyond the former dams shortly after their removal; in 2025, that figure exceeded 13,000. The fish occupied 345 kilometres of previously inaccessible river, returning to 88% of their known historical habitat.
Lead author Damon Goodman said researchers had anticipated the salmon’s return, but not its speed or scale. To reach habitat blocked for about a century, the fish travelled through difficult rapids, constructed fish passages and a large lake. Goodman’s team monitored the autumn migration continuously using a specialised sonar camera near the former Iron Gate Dam site. By producing moving images with sound waves rather than light, the equipment worked despite the extremely muddy water that followed dam removal. Researchers measured individual fish and distinguished Chinook from other species to estimate the number passing the site.
Although Goodman is optimistic about substantial recovery, recolonisation alone does not establish a return to historical population levels. That will require successful reproduction across multiple generations, alongside improvements in habitat, water quality and fish passage throughout the river basin. Scott Hinch, an expert on salmon at the University of British Columbia who did not take part in the research, also called the speed of the return remarkable.
