In a remarkable testament to ecological resilience and dedicated human intervention, Putah Creek in California is experiencing an unexpected resurgence of chinook salmon, a species long absent from its waters. This comeback, far exceeding initial expectations, highlights the profound impact of restoring natural river flows, even in landscapes heavily engineered for human use. While the recent deconstruction of four dams on the Klamath River has garnered significant attention, the story of Putah Creek offers a parallel, perhaps even more nuanced, narrative of riverine rebirth.

Putah Creek, an 85-mile waterway originating in the Mayacamas Mountains and flowing towards the Sacramento River floodplain, has historically been subjected to extensive human manipulation. Its natural course was channelized, its flows drastically reduced by dams and diversions for agricultural and urban water needs, and its banks hardened and straightened. These alterations created an environment inhospitable to native species, leading to the disappearance of salmon and the proliferation of invasive, heat-tolerant fish. The creek’s ecological distress was starkly evident in 1989 and 1990 when sections of its lower reaches dried up entirely, leaving behind a grim tableau of dead fish. The city manager of Davis, through which the creek flows, lamented the severe stress and mortality inflicted upon the local wildlife during these periods.

However, this period of ecological decline sowed the seeds for Putah Creek’s eventual recovery. In 1990, the Putah Creek Council, an environmental advocacy group, initiated a lawsuit against the Solano County agencies responsible for managing the dams. The core of their argument rested on the principle that California law mandates dam operators to maintain healthy conditions for aquatic life. This legal challenge, later joined by the city of Davis and the University of California, Davis, culminated in the 2000 Putah Creek Accord. This landmark settlement required water managers to implement flow regimes that more closely approximated natural patterns, ensuring the creek would no longer dry up during summer months and introducing vital spring pulses to stimulate fish breeding. Crucially, the accord also gambled on the effectiveness of a fall surge of water, termed an "attraction flow," to entice salmon back to the system.

"It was a speculative, ‘Well, maybe this is going to work’ kind of thing," recalled Phil Stevens, executive director of the Putah Creek Council, emphasizing the uncertainty surrounding the initiative. "Nobody knew whether the salmon would come or not."

Despite the success of the Putah Creek Accord in re-establishing a semblance of natural flow, the reality is that approximately 95% of the creek’s water is still diverted for human consumption. Yet, even this comparatively modest release of water, coupled with complementary restoration efforts such as riparian planting and community-led cleanups, has yielded extraordinary results. By 2012, scientists observed a significant recovery of native fish populations, including Sacramento suckers and tule perch, which had regained ecological dominance. The following year marked a watershed moment: eight chinook salmon, drawn by the attraction flows, navigated into Putah Creek, marking the first spawning run in decades. This initial trickle grew to several hundred salmon in 2014 and approximately 1,500 by 2016, prompting the establishment of an annual Salmon Fest in the town of Winters—an event once considered unimaginable. Christine Parisek, a postdoctoral scholar at UC Davis’s Center for Watershed Sciences, views this astonishing comeback as proof that "it’s possible to recover the ecology of a system" by reintroducing natural water flows, a process that, while sometimes lengthy, ultimately proves effective. The fundamental lesson learned is that aquatic life, including salmon, simply requires adequate water to thrive.

As the salmon population in Putah Creek began to grow, a compelling question emerged: from where were these fish originating? Salmon are renowned for their homing instinct, returning to their natal streams to spawn. Given Putah Creek’s long history of being devoid of chinook, the presence of these returning fish suggested they were strays from other river systems. Researchers, including Andrew Rypel, a fish ecologist formerly at UC Davis and now at Auburn University, investigated this mystery. In 2020, their findings revealed that the vast majority of the new salmon population in Putah Creek were, in fact, hatchery-raised fish. During dry years, these fish were transported by truck to the San Francisco Estuary. This unnatural early life experience meant they were not adequately imprinted on their intended home waters. Years later, as adults, they entered the Sacramento River and, by chance, navigated up the Toe Drain, a channelized and warm waterway that eventually led them to Putah Creek. While the tendency of hatchery salmon to stray from their natal rivers is typically viewed as a detriment, potentially diluting the gene pools of wild fish, the situation in Putah Creek was unique: there were no wild fish to compromise.

"If you do the hard habitat work, the hatchery fish can help you," Rypel explained, highlighting how these inadvertently placed fish, when provided with suitable habitat, could contribute to the establishment of a novel population. This marked the emergence of a unique, sui generis population, born from a few disoriented strays.

Further scientific inquiry yielded even more remarkable discoveries. A 2025 study led by Rypel and his colleagues analyzed otoliths—tiny ear bones that grow with a fish—from chinook salmon in Putah Creek. The elemental signatures embedded within these otoliths serve as a historical record of the waters each fish inhabited during its life. The analysis of Putah Creek salmon otoliths revealed that a portion of the fish had not originated from hatcheries at all. Instead, they had been born in the creek itself, migrated to the ocean, and successfully returned as adults, completing their entire life cycle within the restored system. This indicated that the accidental chinook population had begun to shed its domestic origins and truly rewild.

The broader context of salmon populations in California’s Central Valley paints a concerning picture. Declining numbers are a stark reality, driven by the cumulative impacts of dams, water diversions, persistent drought, and other environmental stressors. Projections suggest that by the end of the century, these iconic fish may be extirpated or exist in minimally abundant numbers. Putah Creek stands out as a rare exception, one of the few streams where salmon runs are actually increasing. Max Stevenson, Putah Creek’s streamkeeper—a position established by the accord and funded by the Solano County Water Agency—underscores the importance of embracing all available resources, including hatchery fish, in the effort to restore these populations. "You can go ahead and pooh-pooh the hatchery fish, but it’s all hands on deck," Stevenson stated.

Despite the significant progress, Putah Creek still faces considerable challenges. The creek bed in many areas is compacted or smothered by sediment, diminishing the quality of spawning grounds. Stevenson has undertaken efforts to improve this by using heavy machinery to break up existing gravel and trucking in additional material, but the task remains substantial. A more significant impediment to salmon migration is a 10-foot-high check dam. This structure obstructs passage until late fall, when the irrigation season concludes and water managers remove wooden boards, allowing the chinook to proceed upstream—a rudimentary and outdated method of fish passage. In 2021, heavy rainfall introduced a large amount of organic matter into Putah Creek, leading to low-oxygen conditions that killed incoming salmon before the check dam could be opened, resulting in the loss of nearly an entire year’s spawning cohort. Stevenson is actively pursuing solutions, including the construction of a bypass channel or an underwater fish ladder to enable salmon to circumvent the check dam, or even upgrading irrigation infrastructure to facilitate its complete removal.

The restoration of salmon in such a fundamentally altered environment, according to Rypel, exemplifies "reconciliation ecology"—the practice of creating spaces for nature within landscapes irrevocably shaped by human activity. The chinook salmon of the Central Valley now often rely on artificial environments, such as flooded rice farms for rearing, irrigation ditches for migration, and trucked-in gravel for spawning. These engineered conditions may represent the future for salmon in Anthropocene California, a region where virtually every aspect has been reshaped by human endeavors, yet where, with deliberate effort, space can still be found for these vital aquatic species. As Stevenson eloquently put it, "We can build cities, we can make factories, we can go to the moon. We can make a salmon run here if we want one."