Almost everywhere in California, wild salmon are on the decline. However, one notable exception is Putah Creek, a restored stream winding through the University of California, Davis, campus, where wild salmon are not only increasing in numbers but also managing to complete their life cycle. A groundbreaking study from UC Davis, published in the journal Ecosphere on March 21, 2025, confirms for the first time that some Chinook salmon returning to this creek were actually born there.
Chinook salmon have been observed at Putah Creek since 2014, but earlier studies indicated they were predominantly strays from hatcheries. The latest research, led by UC Davis Professor Andrew Rypel, now reveals a significant breakthrough: 11 of the 407 salmon analyzed were born in Putah Creek, thus completing their full life cycle as wild salmon. "The fact that you have Putah Creek-origin fish is a big deal," Rypel remarked. "To have a growing, stable population that’s natal means it’s a well-managed ecosystem, and that there’s a future for fish in that place. It also shows there’s hope for other streams that are degraded."
The rebirth of salmon populations in Putah Creek can be traced back to a series of ecological restorations initiated after the installation of the Monticello Dam in the 1950s, which had significantly curtailed the creek's water flow. Following a lawsuit in 2000, the Putah Creek Accord mandated year-round water flows, thus reviving a once-thriving ecosystem.
In this rejuvenated habitat, local community members, nonprofits, state agencies, and researchers have collaborated to restore the creek, leading to a resurgence of not only salmon but also insects and songbirds. This vital restoration effort underlines the importance of maintaining healthy ecosystems in the face of climate challenges.
Previously, the presence of salmon at Putah Creek was largely attributed to hatchery strays. Rypel noted, "People began speculating whether any of these Putah Creek-spawning fish were returning to Putah Creek. It was a challenging scientific riddle to figure out.” This riddle was unraveled thanks to the innovative use of otoliths—tiny ear bones from adult Chinook carcasses, which contain chemical signatures that reflect the waters they have traversed.
Through meticulous analysis, the research team discovered that the majority of carcasses analyzed were indeed hatchery-origin salmon; however, the identification of 11 individual salmon that were born in Putah Creek is a pivotal moment in understanding the interaction between hatchery practices and wild fish genetics. Rypel remarked, "The idea that hatcheries can be part of the solution might take people off guard, but there may be positive effects so long as the salmon have a good place to go. There’s a lot of potential to have more Putah Creeks out there."
Yet, the journey of these salmon isn't without peril. Salmon born in Putah Creek face significant obstacles as they migrate to the ocean and attempt to return for spawning. They must navigate through the Yolo Bypass floodplain and into the Sacramento River, proceeding until they empty into the Pacific Ocean. Along this winding path, many obstacles threaten their survival—including restricted fish passage and fluctuating water conditions.
In one notable setback, Putah Creek-origin salmon from 2021 perished before spawning due to an atmospheric river, which caused ammonia-saturated waters to flood into the creek just as salmon were arriving to spawn. Yet, the researchers maintain that collaborative management strategies can mitigate these threats. “There’s so much local love for these fish,” noted Lauren Hitt, a lead author of the study and currently a Ph.D. student at the University of Canterbury in New Zealand. “I hope people recognize that their caring about the system and advocating for the system are what made the changes possible.”
The future of salmon in Putah Creek looks positive, as the local community continues to support efforts to maintain and enhance the creek’s ecosystem. Researchers from UC Davis plan to keep monitoring the salmon as they return to spawn in the fall. This restoration success might indeed offer a template for revitalizing other streams facing similar ecological challenges.
Among the study's contributors were co-authors from various institutions, including Rachel Johnson of National Marine Fisheries Service. Funding for the research came from several sources, including the Solano County Water Agency and California Trout Endowment for Coldwater Fish Conservation.
As for the fall salmon runs? Visitors and community members will have opportunities to witness firsthand the salmon spawning activities across Putah Creek, a testament to the determined efforts of those committed to restoring California's waterways.
