Claire Corlett

Fish Food, Fish Tanks, and More
Fremont Weir Adult Fish Passage Project

Fremont Weir Adult Fish Passage Project


The Yolo Bypass was a historical
floodplain, today it is a resource for people, habitat for fish and wildlife, and
flood protection is the primary purpose of the Yolo Bypass today. It’s 59,000 acres, it’s a pretty large piece of land. It’s 40 miles long, about three
miles wide on average. It collects probably 80% of the floodwaters and
diverts them into the bypass, protecting the city of Sacramento and the
surrounding areas. We have a lot of agriculture in the
bypass, a lot of rice. We have hunting in the bypass, duck clubs. it is a Pacific Flyway hub for waterfowl and shorebirds. It’s a fisheries habitat, so it’s pretty
important. The Yolo Bypass is not only a prominent element of the Sacramento area flood control system, it’s an important fish migration corridor. The Fremont Weir allows for high flows from the Sacramento River onto the bypass, which
occurs in about one out of two or three years. When water spills over the Fremont
Weir, adult Salmon, Steelhead and sturgeon on their way upstream, are often
attracted into the Yolo Bypass. When the Sacramento River falls back
down below the top of the weir, fish become stranded downstream
of this large concrete wall. These fish that have traveled almost 40 miles end up
disconnected from the river. This project focuses on updating the old Denil fish
passage ladder. The problem was when the fish get to the structure, there’s inadequate depth for them to pass through the old structure which was just four
feet wide and six feet deep. So the fish passageway channel now widens that to 15
feet wide and 10 feet deep. The whole system is automated, and once the water
levels get high enough to overflow Fremont Weir, the gate is triggered to
open and allow fish return back to the
Sacramento River. And that connection improves fish passage and reduces their
likely to get stranded in the Yolo Bypass and at Fremont Weir. From a fish’s perspective, when Yolo Bypass floods, the bypass is the river. So a fish coming up the bypass when it’s flooding is moving up towards its spawning
grounds. But as the river starts to drop and the water drops below the crest of that weir, suddenly that water turns off. And where all the fish would have been
attracted up the Yolo Bypass towards Fremont weir, suddenly they’re stuck. And we needed a way to keep enough water moving through that weir, to allow the
fish back to the river. To attract them to that place and put them back where we
want them instead of having them stray into drainage canals and die. And losing
an adult Winter Run, a fish that’s on the brink of extinction is unbearable.
This is a fish that has made it out to the ocean, it’s almost back, it’s almost
there to reproduce, to have five thousand eggs in the gravel, and we’re losing it
because it is attracted to ag flow. If a fish or any other native critter
can’t recognize the river system, the habitat that they’re adapted to, then
they’re not going to do well. So our job is to understand how the valley used to work, what fish expect, and be able to mimic that. To work with nature to allow
Salmon to recognize the Sacramento River again. This project is a prime example of
what we can do when state and federal partners work with local government and
landowners for the benefit of fish and water supply reliability
in California. It’s a big win to have this project completed and we’ve learned
a lot through the implementation of the adult fish passage project and will
continue to use that knowledge as we move forward on future efforts to
address adult fish passage barriers and juvenile floodplain rearing habitat. The
Department of Water Resources and the US Bureau of Reclamation have a large suite
of actions that we need to implement in order to help the recovery of these
species. The overall mission is to promote recovery, so
that we are not causing jeopardy of any of these species when we operate the
State Water Project or the Central Valley Project. That’s the ultimate goal.
We have a long way to go still, and within the bypass there are several
fisheries issues that we need to address as well, but this is a really good start.

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