Risks and Options to Reduce Risks to Fishery and Water Supply Uses of the Sacramento/San Joaquin Delta

California Department of Water Resources (DWR) | January 1st, 2008

Assembly Bill (AB) 1200 (Laird, Chapter 573, Statutes of 2005) highlighted the complex Delta water issues, and directed the Department of Water Resources (DWR) and the De

Assembly Bill (AB) 1200 (Laird, Chapter 573, Statutes of 2005) highlighted the complex Delta water issues, and directed the Department of Water Resources (DWR) and the Department of Fish and Game (DFG) to report to the Legislature and Governor on the following: • Potential impacts of levee failures on water supplies derived from the Sacramento-San Joaquin Delta due to future subsidence, earthquakes, floods, and effects of climate change • Options to reduce the impacts of these factors • Options to restore salmon and other fisheries that use the Delta estuary The State is currently involved in four major planning efforts to evaluate ecosystem and water supply issues and consider options for improvements: 1. The Delta Risk Management Strategy (DRMS) is evaluating Delta issues primarily from the perspective of the risks from levee failures and ways to reduce those risks 2. The CALFED Ecosystem Restoration Program (ERP) Conservation Strategy is identifying restoration opportunities within the Delta and Suisun Marsh ecological restoration zones based on existing elevations, soil types, habitats and natural process requirements of pelagic organisms and other native fish species 3. The Delta Vision will develop a durable vision for sustainable management of the Delta with the goal of managing the Delta over the long term to restore and maintain identified functions and values that are determined to be important to the environmental quality of the Delta and the economic and social well being of the people of the state 4. The Bay Delta Conservation Plan (BDCP) is evaluating Delta issues primarily for the goal of obtaining permits for water supply operations through a comprehensive conservation plan for the Delta designed to protect and restore at-risk species. Since each process has only prepared initial findings at this point in time, this document reports on progress made to define the risks and options to reduce risks for the Delta as requested by the Legislature.

River-Aquifer Interactions, Geologic Heterogeneity, and Low-Flow Management

U.S. Geological Survey (USGS) | ?

Low river flows are commonly controlled by river-aquifer exchange, the magnitude of which is governed by hydraulic properties of both aquifer and aquitard mater

Low river flows are commonly controlled by river-aquifer exchange, the magnitude of which is governed by hydraulic properties of both aquifer and aquitard materials beneath the river. Low flows are often important ecologically. Numerical simulations were used to assess how textural heterogeneity of an alluvial system influences river seepage and low flows. The Cosumnes River in California was used as a test case. Declining fall flows in the Cosumnes River have threatened Chinook salmon runs. A ground water–surface water model for the lower river basin was developed, which incorporates detailed geostatistical simulations of aquifer heterogeneity. Six different realizations of heterogeneity and a homogenous model were run for a 3-year period. Net annual seepage from the river was found to be similar among the models. However, spatial distribution of seepage along the channel, water table configuration and the level of local connection, and disconnection between the river and aquifer showed strong variations among the different heterogeneous models. Most importantly, the heterogeneous models suggest that river seepage losses can be reduced by local reconnections, even when the regional water table remains well below the riverbed. The percentage of river channel responsible for 50% of total river seepage ranged from 10% to 26% in the heterogeneous models as opposed to 23% in the homogeneous model. Differences in seepage between the models resulted in up to 13 d difference in the number of days the river was open for salmon migration during the critical fall months in one given year.

Ruling on Plaintiffs’ Motion for Preliminary Injunction, Case No. Bcv-22-103220-Gap, Bring Back the Kern et al v. City of Bakersfield et al

Superior Court of California, County of Kern | October 30th, 2023

SacPAS Fish Model: A model for emergence, migration and survival of Sacramento River salmon

Delta Stewardship Council (Delta Council) | November 1st, 2017

Sacramento River Temperature Task Group Annual Report of Activities October 1, 2013 through September 30, 2014

Delta Stewardship Council (Delta Council) | October 6th, 2014

Sacramento River Temperature Task Group Annual Report of Activities October 1, 2017 through September 30, 2018

Delta Stewardship Council (Delta Council) | November 21st, 2018

Sacramento River Temperature Task Group Annual Report of Activities, October 1, 2015 through September 30, 2016

Delta Stewardship Council (Delta Council) | October 31st, 2016

Sacramento Valley Salmon Resiliency Strategy June 2017

California Natural Resources Agency (CNRA) | June 2nd, 2017

The Sacramento Valley Salmon Resiliency Strategy (Strategy) is a science-based document that has been prepared by the State of California (State) to address specific near

The Sacramento Valley Salmon Resiliency Strategy (Strategy) is a science-based document that has been prepared by the State of California (State) to address specific near- and long-term needs of Sacramento River winter-run Chinook salmon (winter-run), Central Valley spring-run Chinook salmon (spring-run), and California Central Valley steelhead (steelhead). The Strategy mirrors the approach taken with the Delta Smelt Resiliency Strategy developed by the State in 2016: science-driven, focused, and designed to provide resource agencies, the public, Congress, and the California State Legislature with information critical to collaborative approaches to species resiliency. The Strategy relies heavily on the National Marine Fisheries Service Final Recovery Plan for winter-run, spring-run, and steelhead (NMFS 2014), and is guided by conceptual models of factors driving winter-run population dynamics at key life stages developed by the salmon and sturgeon assessment of indicators by life-stage (SAIL) teams (Johnson et al. 2016; Heublein et al. 2017). The actions are also supported, where indicated, by other salmonid recovery planning documents and efforts. The Strategy is an aggressive approach to improving species viability and resiliency by implementing specific habitat restoration actions. The State will take leadership roles in each action, although in all cases federal and local agency leadership, coordination, and partnerships are required for success. Recent successful restoration efforts led by local agencies and landowners demonstrate the importance and value of these collaborative partnerships. State agencies that could implement this Strategy include the California Natural Resources Agency, the Department of Water Resources (DWR) and the Department of Fish and Wildlife (DFW). The U.S. Bureau of Reclamation (Reclamation) will be a primary partner in many of the actions. In many cases, included actions will benefit an array of aquatic and terrestrial species. Coordination and alignment across various resource management agencies will ensure achievement of maximum public benefit. All of the actions will comply with applicable laws including the U.S. Endangered Species Act (ESA), California Endangered Species Act, California Environmental Quality Act, National Environmental Policy Act, and the federal Clean Water Act.

Salinity Changes the Dynamics of Pyrethroid Toxicity in Terms of Behavioral Effects on Newly Hatched Delta Smelt Larvae

Toxics (MDPI) | February 20th, 2021

Salinity can interact with organic compounds and modulate their toxicity. Studies have shown that the fraction of pyrethroid insecticides in the aqueous phase increases w

Salinity can interact with organic compounds and modulate their toxicity. Studies have shown that the fraction of pyrethroid insecticides in the aqueous phase increases with increasing salinity, potentially increasing the risk of exposure for aquatic organisms at higher salinities. In the San Francisco Bay Delta (SFBD) estuary, pyrethroid concentrations increase during the rainy season, coinciding with the spawning season of Delta Smelt (Hypomesus transpacificus), an endangered, endemic fish. Furthermore, salinity intrusion in the SFBD is exacerbated by global climate change, which may change the dynamics of pyrethroid toxicity on aquatic animals. Therefore, examining the effect of salinity on the sublethal toxicity of pyrethroids is essential for risk assessments, especially during the early life stages of estuarine fishes. To address this, we investigated behavioral effects of permethrin and bifenthrin at three environmentally relevant concentrations across a salinity gradient (0.5, 2 and 6 PSU) on Delta Smelt yolk-sac larvae. Our results suggest that environmentally relevant concentrations of pyrethroids can perturb Delta Smelt larvae behavior even at the lowest concentrations (<1 ng/L) and that salinity can change the dynamic of pyrethroid toxicity in terms of behavioral effects, especially for bifenthrin, where salinity was positively correlated with anti-thigmotaxis at each concentration.

Salton Sea Exceedances of California’s Air-Quality Standards Highlight Governance Gaps and Monitoring Needs

University of California, Los Angeles (UCLA) | September 4th, 2025

The Salton Sea region is known for its poor air-quality, which is often linked to dust and contributes to alarmingly high rates of respiratory problems among residents. H

The Salton Sea region is known for its poor air-quality, which is often linked to dust and contributes to alarmingly high rates of respiratory problems among residents. However, air-quality issues extend beyond dust. Residents also face the distressing reality of frequent hydrogen sulfide (H2S) emissions. Depending on individual experiences, these emissions can range from uncomfortable to severely suffocating. To gauge the severity of these concerns, the Salton Sea Environmental Timeseries (SSET), a community-based research group, recently installed two hydrogen sulfide monitors in the area. Their data indicates that H₂S emissions consistently exceed the California Air Resources Board state standard of 30 parts per billion (ppb), with 243 hours above this threshold recorded between May and September 2024 alone. Existing government air-quality monitors, located north of the Salton Sea, primarily detect H₂S only when winds blow from the southeast, whereas SSET data show elevated emissions occur regardless of wind direction. This highlights a critical gap in the current government monitoring network, which fails to capture the full scope of H₂S pollution. As more data highlight connections between water and air-quality, it is crucial to monitor air-quality in all its aspects, not just those related to dust. The Salton Sea region has a predominantly low-income Latinx, immigrant, and Indigenous population across two California counties. The persistent issue of hydrogen sulfide pollution serves as a clear example of environmental injustice. For over two decades, the state and federal governments have been legally obligated to restore the Salton Sea—meeting that obligation today means pairing public health action with robust monitoring.