Monitoring of Yolo and Sutter Bypasses for Fish Stranding and Rescue Operations

During high outflow events, the Sacramento River’s floodwaters overtop Fremont and Tisdale weirs, resulting in inundation of the Sutter and Yolo Bypasses. These flows attract upstream migrating fish from the Sacramento River into the Yolo Bypass at the mouth of the Cache Slough complex near Liberty Island. However, when floodwaters recede, numerous fish can be trapped in the downstream of the Fremont Weir splash basin and in downstream scour ponds, pools, and swales and are unable to return to the Sacramento River. CDFW staff has conducted numerous fish rescues at the Fremont Weir, Yolo Bypass and Tisdale Weir, and other flood control structures, saving tens of thousands of fish including numerous individuals of the aforementioned listed species.
  • View of Fremont Weir Denil fish ladder during overtopping event in January 2006. Flash boards are left in place until overtopping of the weir ceases.
  • View of Fremont Weir Denil fish ladder after cessation of an overtopping event in March 2016. Note that flash boards have been removed to facilitate fish passage through the weir.
  • View of an oxbow pond south of the west section of the Fremont Weir. Bank gradient and presence of woody debris reduce the likelihood of rescuing fish isolated within this feature. Photo taken 5 October 2015.
  • View isolated pool southeast of the Fremont Weir. An adult green sturgeon is visible in the upper portion of the photo.
  • View of the “Tule Pond” in the Yolo Bypass southeast of the Fremont Weir. Sturgeon, Chinook salmon, steelhead, and other fish species may become isolated within the Tule Pond when hydrological connectivity to the Tule Canal is lost during receding flows.
  • Adult white sturgeon rescued from the Tule Pond receiving an acoustic transmitter.
  • Close-up view of temporary fish barrier deployed at the fishway on the east section of Fremont Weir. The barrier is constructed of specially designed crowder racks and ¼ inch mesh beach seine. Photograph taken 14 March 2017.
  • West section of Fremont Weir prior to 4 May 2017 fish rescue. Photograph taken 4 May 2017.
  • Green sturgeon rescued from west Section of Fremont Weir being released into the Sacramento River. Photograph taken 4 May 2017.
  • View of scour pool approximately 30 m southeast of the Fremont Weir Denil fish ladder. Hatchery origin Central Valley steelhead and fall run Chinook salmon were rescued from this pool on 15 March and 5 April 2017. Photograph taken 15 March 2017.
  • Sothern DPS green sturgeon rescued from Tisdale Weir on 11 May 2017. Note abrasions on the snout. Similar abrasions and abrasions to eyes, fins, and ventral scutes were observed on green sturgeon and white sturgeon rescued from the Fremont Weir. Photograph taken 11 May 2017.
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