Fish get a boost in the Yolo Bypass

Salmon and other anadromous fish received a boost this year with the construction of fish passage projects in the Yolo Bypass.

aerial view of construction
Construction of the Wallace Weir Fish Rescue Facility, November 2016 (source: Reclamation District 108)

The Wallace Weir Fish Rescue Facility, completed in early 2018, was designed, permitted, and constructed in just over two years. Originally an earthen berm installed to create an irrigation backwater, the temporary weir served an essential function by blocking access to the Colusa Basin Drain for fish migrating upstream. The Colusa Basin Drain, a large floodplain between the Coast Range and the Sacramento River, has no return passage to the Sacramento River or Yolo Bypass and serves as a dead-end for salmon migrating upstream. During flood events, however, the earthen berm would fail, allowing fish to stray into the dead-end area through the Knights Landing Ridge Cut.

As the result of a public-private partnership between the Department of Water Resources, State Water Contractors, Reclamation District 108, and local agricultural landowners, a permanent weir with an inflatable dam and positive fish barrier has been constructed, along with a fish rescue facility operated by California Department of Fish and Wildlife to capture and return straying fish. This multi-benefit project will also maintain appropriate irrigation water surface elevations for farms in the Colusa Basin Drain, without impeding outflows during flood season.

Completed Wallace Weir in April 2018 (source: Friends of the San Francisco Estuary)

For more on this project, visit Reclamation District 108’s project page, and read about a visit to the completed project by our partners at Friends of the San Francisco Estuary earlier this year.


This year also marked the beginning of construction on the Fremont Weir Fish Passage Modification Project in the upper Yolo Bypass. Constructed almost 100 years ago as a flood control project, the two-mile weir has an undersized fish ladder in place, which creates a challenge for adult salmon and a barrier for adult sturgeon migrating upstream. The project, funded by the U.S. Bureau of Reclamation and Department of Water Resources, and supported by non-governmental organizations and landowners, will include replacement of an earthen agricultural road crossing with a permanent bridge or other fish-friendly crossing, removal of a second earthen agricultural road crossing, channel modification immediately upstream and downstream to improve migratory fish passage, and replacement of the existing fish ladder with a wider and deeper passage structure.

In the Google Maps screenshot above, the existing Fremont Weir is the thin horizontal line indicated by the red arrows.

These two projects fulfill the milestone under Task 12-2 and mark completion of this task; however, more work is underway through EcoRestore.

TASK 12-2: Advance a multi-benefit project in the Yolo Bypass by establishing a common vision for improvements supported by local, state, and federal agencies.

BY 2017: Initiate construction of multiple fish passage improvement projects within the Yolo Bypass.

Stay tuned for updates on the Lisbon Weir Fish Passage Modification Project in the mid-Yolo Bypass area, and of course the  Yolo Bypass Salmonid Habitat Restoration and Fish Passage Project, which eventually could open up to 17,000 acres of floodplain to fish passage.