In 2024, four Klamath River dams collapsed, reopening habitat blocked for more than a century; In two salmon runs, 21,052 Chinook moved upstream and regained 88% of their historic range.

Four concrete barriers blocked the path for salmon that once swam freely between the Pacific Ocean and the high desert areas of Oregon and California for more than a hundred years. The dams were removed in 2024 as part of one of the largest dam removal projects in U.S. history, allowing the river to flow freely for the first time in generations. The results were quick and surprising. In just two salmon runs, more than 21,000 Chinook salmon moved upstream, accessing 88 percent of the range they historically occupied before dams were built. As detailed in investigation Titled ‘Rewilding the Upper Klamath River Basin’ published in Nature, the fish’s rapid return offers powerful evidence of how quickly ecosystems can begin to heal when key obstacles are removed.A cut riverThe Klamath River stretches more than 400 kilometers from the high lakes of southern Oregon to the Pacific coast of northern California. For thousands of years, it supported one of the most productive salmon areas on the West Coast. Chinook, coho, and steelhead traveled hundreds of miles inland to spawn in cold, clear tributaries, supporting rich food webs and indigenous communities along the way.That changed in the early 20th century, when a series of hydroelectric dams were built in the lower Klamath. Four of these dams, built between 1903 and 1962, created a chain of reservoirs that flooded river canyons and blocked the passage of fish. The salmon could no longer reach the upper reaches of the basin. Their numbers declined dramatically, and with them disappeared the cultural practices, commercial fishing, and ecological functions that had long depended on the annual pulse of returning fish.A decision to remove damsFor decades, tribal nations, fishing groups and conservation organizations called for the dams to be removed. They argued that the structures were obsolete, economically marginal and ecologically destructive. The reservoirs trapped sediment, warmed the water, and created favorable conditions for algae blooms and fish diseases. Meanwhile, the dams prevented salmon from accessing hundreds of kilometers of spawning and rearing habitat.After years of negotiation, regulatory approvals and planning, the decision was made to decommission the four lower Klamath dams. Crews began removing concrete barriers, draining reservoirs, and beginning river channel restoration work beginning in 2023 and ramping up through 2024. By the end of 2024, the Klamath was flowing freely from its headwaters to the sea for the first time since the early 20th century.Return of salmon in forceWith the barriers removed, the question on many minds was how quickly the salmon would respond. Fish biologists and tribal monitors installed count dams, cameras and survey stations along the river and its tributaries to track returning adults. The first comprehensive analyzes following the dam’s removal provided a clear answer.On the two post-removal salmon runs, a total of 21,052 adult Chinook salmon were documented moving upstream past former dam sites. These fish traveled far beyond the reservoirs that had once trapped them, reaching spawning grounds in the Upper Klamath Basin that had been inaccessible for more than a century. Based on historical records and habitat maps, researchers estimate that this move allowed Chinook to regain about 88 percent of their historical range in the watershed.What do the numbers mean?The return of more than 21,000 Chinook in just two races is significant for several reasons. First, it shows that adult salmon were able to find and use the newly opened habitat almost immediately. There wasn’t much delay as the river adapted or as the fish “learned” new routes. The instinctive urge to return to the natal currents seems to have guided them successfully once the physical barriers disappeared.Second, the magnitude of the range recovery is notable. For generations, Chinook were confined to the lower reaches of the Klamath and some tributaries below dams. They can now spread across the upper basin again, using a much wider range of streams, side channels and floodplain habitats. This spatial diversity is critical for resilience because it spreads risk across different environments and reduces the chance that a single event, such as a heat wave or disease outbreak, will wipe out the entire journey.Third, the figures suggest that the population has more room to grow. With much more habitat available, the river can potentially support larger courses in the future, as long as other stressors such as water quality, ocean conditions, and harvest are carefully managed.Benefits beyond salmonThe return of the Chinook to the upper Klamath isn’t just a victory for the fish. It spreads throughout the ecosystem and human communities linked to the river. Salmon carry nutrients from the ocean to inland waters and forests when they spawn and die. Those nutrients feed insects, birds, mammals and plants, increasing productivity across the landscape.The return of salmon has deep cultural and spiritual significance for tribal nations along the Klamath. It is now possible to revitalize fishing ceremonies, traditional diets and intergenerational knowledge that were disrupted by dams. Commercial and recreational fisheries may also benefit over time as fisheries rebuild, supporting local economies that have struggled through decades of low returns.From a river health perspective, dam removal has already begun to change the physical character of the Klamath. Sediment that had been trapped in reservoirs is moving downstream, rebuilding gravel bars and spawning beds. With the return of the river’s more natural flow regime, water temperatures should cool, providing better conditions for salmon eggs and juveniles.A faster recovery than expectedOne of the most surprising aspects of the Klamath story is the speed of the response. It is often assumed that large-scale ecosystem restorations take decades to show significant results. In this case, measurable gains in fish distribution and habitat access occurred just one year after dam removal.Scientists warn that the work is not finished. Long-term monitoring will be necessary to track how juvenile salmon survive, how ocean conditions affect returns, and how the river channel continues to adjust. Climate change, water management and land use in the basin will influence the trajectory of recovery. But early data makes clear that removing the right barriers can generate quick and substantial benefits.Lessons for other riversCommunities and policymakers across the country are closely monitoring the removal of the Klamath Dam. Hundreds of aging dams dot American rivers, many of them no longer economically viable and some blocking critical fish habitat. The Klamath experience suggests that when dams are removed carefully and in coordination with tribal partners, regulators and scientists, the ecological benefits can be large and rapid.It also highlights the importance of setting clear goals and investing in follow-up. The ability to document that 21,052 Chinook regained 88 percent of their historic range did not happen by chance. It required coordinated field work, data sharing and analysis that can now inform future restoration projects.A river that runs free againToday, along the banks of the Klamath, the silhouettes of ancient reservoirs can be seen in the wide, silt-filled valleys, but the river itself is no longer impounded. It runs through old dam sites, carving new channels and reconnecting with floodplains that have waited for generations for this moment.In the water, signs of life are returning. Salmon are moving upstream in numbers never seen before, reaching spawning grounds that their ancestors used before the first concrete was poured. For the people who have fought for this result, what has been seen is both a validation and a promise. It shows that even after a century of damage, a river can begin to heal and the creatures that depend on it can return home.