Study Shows Natural Flow Regime Can Restore Native Fishes to Putah Creek

New scientific research shows that manipulating stream flows with only small amounts of additional water can restore native fish to habitats from which they had largely disappeared. According to a paper recently published in the scientific journal Ecological Applications, a more natural flow regime was effective in restoring native fishes such as pikeminnows, tule perch, and Sacramento suckers in lower Putah Creek, a tributary of the Sacramento River.

The paper, “Restoring Native Fish Assemblages to a Regulated California Stream Using the Natural Flow Regime Concept” by Joseph Kiernan, Peter Moyle and Patrick Crain shows that restoration of native fish populations was facilitated by managing creek flows to create favorable spawning and rearing conditions, cool water temperatures, maintaining flowing conditions over the length of the creek, and displacing non-native species with naturally occurring high-discharge events.

“This important study demonstrates that moving toward a more natural and functional flow regime can effectively restore native fish populations and reduce the abundance of non-native fishes in regulated rivers,” said Peter Goodwin, Lead Scientist of the Delta Science Program.

Restoration of native fishes in the studied ecosystem was largely achieved through manipulating stream flows at biologically important times of the year, only requiring a small increase in the total volume of water delivered downstream during most water years.

“I like to think of it as a good demonstration that reconciliation ecology (the science of inventing, establishing and maintaining new habitats to conserve species diversity in places where people live, work or play) can work,” said Peter Moyle, one of the paper’s authors and a professor of fish biology at the University of California, Davis, who has been conducting research in the Putah Creek area for more than 30 years.

Putah Creek is a sliver of habitat flowing through an agricultural landscape, but the creek was pretty much ignored in the 1970s. “It was where you tossed your trash and told your kids not to go to because they might get hepatitis if they swam in the water,” Moyle said. “It was not a system anyone appreciated; it was pretty much overwhelmed with non-native species.”

But in the late 1980s the creek dried up from drought-a key event that got people together as they suddenly realized there was more to this creek than they had thought. That resulted in a lawsuit; the University of California, Putah Creek Council and City of Davis sued Solano Water Agency to keep water in the creek for the fish. A flow regime for the creek was designed as part of the 2000 settlement agreement with Solano Water Agency.

“Once we got the flow regime, the native fishes did come back very quickly,” Moyle said. “There’s now a long section of the creek dominated by native fish which was not the case initially.”

Moyle started sampling Putah Creek with his classes in 1978, which gave him a data set on fish abundance long before the lawsuit was even a thought in anyone’s mind. Before the trial began, the fishes of the creek were sampled for several years. These data sets helped to demonstrate that a natural flow regime would work. “We have data before and after the settlement agreement,” he said. “What makes this paper so special is that by having before and after data we can document the rapid change to the creek. Usually you do something and then you start collecting data.”

Solano Water Agency is now a major supporter of restoration of the creek, giving even more water than was required in the lawsuit. The agency agreed to pay for monitoring of the creek; not just for fish, but also for birds and mammals.

“The agreement created the conditions that favor the natives and make it harder for non-natives to reproduce,” Moyle said. “We have to keep managing the creek. If we suddenly let it go, the non-natives would be back in spades. You’re never going to get rid of the non-native species. The non-native organisms will always be part of the system. But you can keep them at bay.”


“We have to keep managing the creek. If we suddenly let it go, the non-natives would be back in spades.”

--Peter Moyle, Professor of Fish Biology at U.C. Davis


Not only have the native fish recovered, but there are also lots of projects to improve the creek for birds, mammals, and native plants. The city of Winters now has a major park along Putah Creek and there’s a lot of community-level support for the creek.

“It’s a much better place for native fish and for people to recreate,” Moyle said, adding that Putah Creek is an “amazing” place for owls and hawks-10 percent of all Swainson’s Hawks in California are found next to the creek.

Putah Creek is now a place to be proud of, but Moyle’s work is not done. He and his colleagues will continue their research on restoration and natural flow regimes.