Yolo Bypass Salmonid Habitat Restoration and Fish Passage

fremont weir

The lower Sacramento River has experienced decreased habitat quality and fish have experienced inadequate access to higher quality habitat. Reclamation and the California Department of Water Resources (DWR) are seeking to improve fish passage and increase flood plain rearing habitat in the Yolo Bypass.

The Yolo Bypass is a leveed 59,000-acre engineered floodplain near Sacramento. It is California's largest contiguous floodplain and provides valuable habitat for a wide variety of aquatic and terrestrial species (Sommer et. al. 2001b). The Yolo Bypass experiences inundation in about 70 percent of years through overtopping events at Fremont Weir and flows from west side tributaries. The bypass is about 40 miles long, reaching from near Knights Landing down almost to Rio Vista.

Fremont Weir

The Fremont Weir (pictured above), at the northern end, is a 1.8-mile-long concrete structure designed to allow flow into the Yolo Bypass during high-flow events when the Sacramento River is higher than the weir's 32-foot weir crest elevation. The weir has a concrete stilling basin just downstream of the crest and along its full length to minimize scouring during overtopping events. Once the Sacramento River recedes below the crest of Fremont Weir, fish are likely to become stranded in the stilling basin.


The Project is in accordance with Reasonable and Prudent Alternative (RPA) actions I.7 and I.6.1, in the 2009 National Marine Fisheries Service Biological Opinion (2009 NMFS BO) on the Long-Term Operations of the Central Valley Project and State Water Project.

The Project would primarily consist of a new Fremont Weir headworks structure, a new outlet channel, and downstream channel improvements.
















Project map

Yolo Bypass Salmonid Habitat Restoration and Fish Passage EIS/EIR

Yolo Bypass Salmonid Habitat Restoration and Fish Passage Project Data Viewer:  DWR and Reclamation created the Data Viewer as a platform to view modeled results of how increased flows may affect inundation within the Yolo Bypass. The Data Viewer is publicly accessible and provides hydrodynamic modeling results and maps for any selected assessor parcel in the Yolo Bypass.

Working Group

The materials presented below are draft and preliminary and, as such, Reclamation and DWR make no warranties, representations or guarantees, either expressed or implied, as to the completeness, accuracy or correctness of the data nor accepts or assumes any liability arising from its use.

Scoping Materials - 2013

Implementation Plan - 2012


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Last Updated: 11/30/18