Department of Water Resources Home
YBFMP - What is the Yolo Bypass?
AES Banner

Yolo Bypass Fish Monitoring Program: What is the Yolo Bypass?

Largest off-channel floodplain in California ‘s Central Valley

Located west of the city of Sacramento adjacent to the Sacramento River, the Yolo Bypass is a 24,000 hectare floodplain that doubles the wetted surface area of the Delta when fully inundated. Although originally engineered as part of the Central Valley Flood Control System, the Bypass is also utilized for agriculture from spring through early fall, and provides vast floodplain habitat for birds and fishes during the winter and early spring.

Yolo Bypass Map


Basic Hydrology

The Yolo Bypass floods in approximately 60 percent of years when high Sacramento River waters crest over the top of Freemont Weir at the northern end. “Overtopping” is most frequent from January-March but has occurred as early as October and as late as June. Localized flooding can also originate from four small western tributaries: Cache and Putah creeks; Willow Slough; and the Knight's Landing Ridge Cut from the Colusa Basin. The Toe Drain canal on the eastern edge of the floodplain drains the bypass following inundation events, and remains wetted year-round as a tidal dead-end slough.



Delta SmeltSplittailChinook


The Yolo Bypass is an important habitat for many fish species. Forty-two species have been documented utilizing the floodplain, including endangered Delta smelt (Hypomesus transpacificus), the floodplain spawning Sacramento Splittail (Pogonichthys macrolepidotus), and federally-listed Winter and Spring Run Chinook salmon (Oncorhynchus tshawytscha). The Yolo Bypass also supports high phytoplankton and drift invertebrate production that can subsidize the estuary downstream.

…Link to journal article with more background  on the Yolo Bypass