Yolo Bypass Salmonid Habitat Restoration and Fish Passage

fremont weir

A prominent element of California’s flood control system and a critical migration corridor for fish.

The Central Valley used to be a vast system of wetlands, tidal marsh and floodplains, which allowed juvenile fish to move through the Sacramento River to the food-rich floodplains. As floodplain habitats diminished over time, fish were disconnected from their food source.

Reclamation and the California Department of Water Resources (DWR website) are partnering to reconnect floodplain habitat and improve fish passage for young salmon. The Yolo Bypass Salmonid Habitat Restoration

Project works to reconnect the floodplain for fish during the winter season and improve connectivity within the bypass and to the Sacramento River. The project provides seasonal inundation that mimics the natural process of the Yolo Bypass floodplain and improves connectivity within the bypass and to the Sacramento River.

The project primarily consists of a new Fremont Weir headworks structure, a new outlet channel, and downstream channel improvements. This enables juvenile salmon to feed in a food-rich area for a longer time, allowing them to grow rapidly in size and improving their chances of survival as they travel to the ocean. Improvements will also reduce stranding and migratory delays of adult salmon and sturgeon due to passage barriers.

The Project is included in Reclamation’s 2019 Proposed Action for the Long-term Operation of the Central Valley Project and the State Water Project, adopted in the 2019 National Marine Fisheries Service (NMFS) biological opinion, and included in the Reclamation’s 2020 Record of Decision. The NMFS biological opinion includes non-discretionary measures known as Reasonable and Prudent Measures (RPM). The terms and conditions of RPM1(g) states “Reclamation shall complete construction of the Fremont Weir component of the Yolo Bypass Salmonid Habitat Restoration and Fish Passage Project by 2022.

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.

Environmental Impact Statement/Environmental Impact Report

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: 6/7/21