Recent rains are helping boost some California salmon populations. Here’s how.

The impacts of a wet season in California can be far-reaching — they're dangerous and can be destructive.

But the water dumped on the state is essential to supplying some 40 million Californians with everyday necessities and bolstering the state's billion-dollar agricultural industry. 

There's another essential but easily overlooked benefit to an exceptionally wet winter. The Yolo and Sutter bypasses were designed for flood control, diverting water and, in turn, creating a floodplain. It's great for us humans, but it's also a feast for wildlife.

It's easy to notice the abundance of birds hanging along these waterways on their annual Pacific Flyway journey, but underneath the surface, millions of juvenile salmon are bulking up for their trip to the Pacific Ocean before coming back to freshwater to spawn.

To learn more about how the bypass floodplains are helping salmon, CapRadio's Vicki Gonzalez spoke with UC Davis Center for Watershed Sciences Field and Lab Director Carson Jeffres about what the wet season has done for fish.

This interview has been edited for clarity and length.

On the importance of salmon in California

Salmon in California are really interesting because we're at the southern end of their distribution, so we're at the very edge of where they live in the Pacific. Because of that, we have very unique fish. We have four [migration] runs of Chinook salmon in California, which is different than anywhere else. We have a very intimate kind of cultural respect for them. 

They've diversified throughout the state, but they're struggling, and that's one of the things that we're working on.

On the function of Yolo and Sutter bypasses

The Yolo and Sutter bypasses are both on the Sacramento River. If you drive from Davis to Sacramento, you drive over the Yolo bypass, and oftentimes most of the years, it looks like agricultural fields. It’s rice, it’s wetlands. Now you drive over it, it looks like a big lake.

There’s so much water that comes out of the Sacramento River, and that’s really what saves Sacramento. The city of Sacramento wouldn’t be here without the Yolo and Sutter bypasses that reroute the water around that river.

Baby salmon are born higher up in the rivers, and they take this path down the Sacramento River, it’s like a freeway for them … and then these bypasses in the other floodplains are like bed and breakfast for them on that migration out. It’s a place where they can stop, they can get some food — they grow really fast — and they keep on going on their way out to the ocean.

On how Northern California's salmon are doing this season

We’re out looking in the rivers, and we’re looking on the floodplains and we’re seeing nothing but big fat salmon. These are the salmon that you really want to see, and these are likely the same that we would have seen historically before we put levees on the river and kind of divorced the floodplain from the river.

So when the water spreads out and goes out across the byway, it actually slows down. If you drive over the bypass, it’s hard to see that the water’s even moving, right? If you drive over the Sacramento River, it looks like a current that’s going by.

And what happens is that water slows down, the sediment in there settles out. You have lots of photosynthesis and lots of zooplankton and phytoplankton, and the fish just gorge on that food. 

There’s about 100 times more food in the Yolo bypass than [there] are [elsewhere]. It’s a little warmer, and then the fish grow about eight times faster on the Yolo bypass than they do in the river.

On the impacts of the state having too much water

It’s a double-edged sword — by having lots of water in these wet years, as we’re realizing now, we see flooding in the Tulare basin. We’ve seen levee failures in various systems. 

It really highlights the multiple benefits of having these large flood control structures that have an ecosystem benefit as well. When levees fail and lands are flooded, there’s a big cost to that. And one of the best mitigations for that — particularly if we see an ever-changing climate with more extreme precipitation events — is having floodplains that really have the ability to reduce that flood risk.