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January 10, 2018  |  Written by Alyson E. Ackerman

Draft Environmental Document Released for Yolo Bypass Salmonid Habitat Restoration and Fish Passage Project

Just before the New Year, the United States Bureau of Reclamation (Reclamation) and the California Department of Water Resources (DWR) released the Draft Environmental Impact Statement/Environmental Impact Report (DEIS/EIR) for the Yolo Bypass Salmonid Habitat Restoration and Fish Passage Project.  The Project seeks to address the negative effects that development of the Central Valley’s flood control system has had on the habitat for various fish species.  The Project is expected to beneficially impact the fish species in the Yolo Bypass and other water bodies within the Project area.  Such beneficial impacts include increased fish passage conditions, increased food resources, and improved habitat conditions.  While the Project will have some adverse water quality effects in the Bypass and downstream, these effects are not expected to substantially affect fish species.

Comments on the DEIS/EIR are due February 15, 2018.


The Yolo Bypass is an engineered floodplain located west of Sacramento.  It is a 59,000-acre area containing numerous forms of infrastructure, such as weirs, canals, drains, and ponds which control the floodwaters of the Sacramento River.  In addition to diverting water from the delta cities, the Bypass is home to a host of wildlife and aquatic species and boasts rich soil for agricultural uses.  The Bypass is also part of two large water conservation and management systems:  the Central Valley Project (CVP) managed by Reclamation, and the State Water Project (SWP) managed by DWR.

The purposes of the CVP and SWP are vast and multidimensional.  Generally, both provide water for agricultural and municipal purposes throughout the state by moving and storing water from north to south.  A 2009 Biological Opinion issued by the National Marine Fisheries Service concluded that changes to CVP and SWP operations were necessary to protect critical habitats for various species listed under the Federal and/or California Endangered Species Acts, including Sacramento River winter- and fall-run Chinook salmon, Sacramento splittail, Central Valley spring-run Chinook salmon, Central Valley steelhead, and Southern Distinct Population Segment (DPS) of North American green sturgeon.

The Project

The Salmonid Habitat Restoration and Fish Passage Project seeks to improve fish species’ accessibility to the higher quality habitat of the Yolo Bypass by increasing the floodplain’s inundation and improving the connectivity of water passage structures between the Bypass and the Sacramento River.  The DEIS/EIR evaluates six action-alternatives to achieve these ends, each of which would install one or more gated notches in Fremont Weir.  The placement and elevation of these notches varies from alternative to alternative, along with the volume of flows (ranging from 3,000 – 12,000 cfs); all would allow water to enter the Bypass from the Sacramento River when the river’s water level is not high enough to crest Fremont Weir (an elevation of 32 feet).  Additionally, all action-alternatives would involve construction of a supplemental fish passage facility at a different location on Fremont Weir.  The California Environmental Quality Act proposed project (Alternative 1) would allow for 6,000 cfs of bypass flows to enter the Yolo Bypass from a notch on the east end of Fremont Weir at an elevation of 14 feet during November through March 15.

Key DEIS/EIR Findings

According to the DEIS/EIR, the increased flows under all Alternatives of the Project will have a less than significant impact on water deliveries to CVP and SWP contractors, both north and south of the Delta, with changes to water deliveries being less than one or two percent (depending upon Alternative).  The Project will, however, reduce surface water flows in the Sacramento River between Fremont Weir and the Delta, which could affect the quantity of water available for diversion through the intakes for the proposed California WaterFix project.

The Project is expected to result in a significant impact on water quality within the Yolo Bypass and downstream, particularly with respect to methylmercury.  According to the DEIS/EIR, the increased flows to the Yolo Bypass may result in increased production of methylmercury, which could result in greater amounts of the compound entering the food web, although there was insufficient data available to determine the extent and effect of such an increase on the food web.  Development of a water quality mitigation and monitoring program is proposed for each Alternative to reduce increases in water quality constituents; however, increased methylmercury production in the Bypass would remain a significant and unavoidable impact.  Notwithstanding the potential increased production and concentration of methylmercury, the increase is expected to have a less than significant impact on fish species in the Bypass and downstream.

With respect to agricultural impacts, construction of the various Project structures would necessitate the conversion of some agricultural land to nonagricultural uses, resulting in losses to grazing land and potentially reduced crop yields.  The extent of agricultural land permanently affected by the Project depends upon the Alternative, ranging from 30 acres to 101 acres.  According to the DEIS/EIR, all of the Alternatives would have a less than significant impact to agricultural land use except for one, which would have a significant impact and require mitigation.  The increased inundation of the Yolo Bypass may also prolong the duration in which the agricultural fields therein remain wet, which may delay the start of the planting season and could cause losses to crop yields.

Public meetings on the Project are scheduled for Wednesday, January 17, 2018, at 6:00 p.m. in Woodland, and Thursday, January 18, 2018, at 1:30 p.m. in West Sacramento.  Written comments are due on February 15, 2018.  The complete DEIS/EIR is available here.

For more information on the Project and implications on changes in water deliveries or water quality and its concomitant impacts on fish species, please contact Alyson Ackerman at

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