A Chico nonprofit is restoring habitat along the Sacramento River to help improve the chance of survival for young salmon.
Chinook salmon are the only salmon species that live in the Sacramento River. They’re also an indicator species, meaning their presence signals how healthy a river is. That’s bad news for the Sacramento River, because chinook populations are threatened and have been declining drastically for decades.
What’s being done
A central reason for the decline of salmon has to do with changes to the river’s flow from dams and levees that were built for farming irrigation, power generation and flood control.
The Sacramento River used to flood its banks when the area got a lot of rain. Seasonal flooding would then fill underground aquifers with water while spreading sediment and nutrients around the entire Sacramento Valley. This natural cycle is the reason the valley is one of the most productive agricultural regions in the world.
Michael Rogner is the associate director of restoration science at River Partners. He said rivers that have been constrained have had the flow of sediment downstream disrupted.
“Which is essentially what makes the river, you know, water and movement of sediment across the floodplain,” Rogner said. “And so the result that happened is it totally changed the flooding dynamics.”
Rogner explained that the sediment deposits help create a braided, complex ecosystem. Without that natural process, the river carves a deeper channel into the floodplain instead of moving around in a more natural way.
River Partners is working with the Mechoopda Tribe at a site called Indian Fisheries on a project to help young salmon find their way back into the river by reconnecting side channels along the river.
Jennifer Rotnem, a restoration ecologist working on the project, said side channels are crucial to a young salmon’s survival.
“Side channel restoration is essentially reestablishing those smaller channels within the river system that branch off from the main stem of the river, and these channels provide critical habitat for fish, particularly juvenile salmon,” Rotnem said.
After recent rains the river went up more than 15 feet in this area, temporarily flooding water into the side channels. When the water levels subsided, the side channels were cut off, forming pools called oxbows.
Reconnecting oxbows to help salmon survive
“The pond that we're looking at, or the oxbow that we're looking at, is full of baby salmon right now, because we had this high flow a couple weeks ago,” Rogner said. “There’s probably several thousand baby salmon in there right now.”
The pools are an ideal habitat because they contain more food than the main river channel. That means juvenile salmon are able to eat a lot and grow faster.
“The bad news is that unless there's another flood that comes along and flushes this out, none of these salmon are gonna survive,” Rogner said.
Juvenile salmon need to get back into the main river in order to make it out to the ocean, where they will mature into adults.
Salmon have a complex life cycle. Once they travel to the ocean, they spend about three years there before returning to their native watershed to breed and lay eggs. This return is crucial to the survival of the species.
“What determines if this fish is going to come back three years from now and breed somewhere in the upper watershed is largely, how big is it when it gets to the Golden Gate,” Rogner said. “You know, how big is it when it gets down to the bottom end of the system?”
Once these salmon get to sea, they become prey for larger ocean fish, Rogner said. But when they are bigger, fewer fish are capable of eating them and their chances of survival increase.
Rogner said this critical early stage in the salmon’s life cycle has been affected the most by levees and dams.
“One of the things that constraining rivers has done is it’s made it so that juvenile fish have a really hard time getting out to the Golden Gate, and when they get there, they're very small,” Rogner said. “And so what we're trying to do is we're giving them the body size and the ability to survive the coming three years, so they can come back.”
Challenges to the restoration process
One of the challenges is finding where natural floodplains are, and where levees can be removed without affecting nearby towns and farms.
“How do we bring back a more dynamic river system and a place where people live, you know? And that's the hard part, because you have levees that protect houses, you have levees that protect cities,” Rogner said.
River Partners identifies areas that are safe to let flood, such as Indian Fisheries. When they remove levees in these places, it can help prevent downstream flooding during storms.
Rotnem said the river needs space to overflow onto the floodplain, “Both to prevent flooding further downstream, but also to create habitat for the fish and wildlife that historically have depended on those areas.”
Rotnem added that farmers near the river have sold some sections of their land to River Partners to be put into restoration.
“Our projects mostly occur on the wet side of the levee in areas where farm production’s been challenging due to interactions with the river and it's been difficult to farm those areas at a profit, and so oftentimes the farmers are happy to sell their land and happy to see it move into conservation, because it's not very productive as farmland,” Rotnem said.
Only 5% of natural river habitat still remains in the Sacramento Valley.
River Partner’s goal is to restore 30,000 acres of river habitat in California by 2030. They’ve restored about 20,000 acres so far.
