Salinity

The Measure

Water management agencies comply with State Water Resources Control Board objectives for salinity in the Delta for D-1641 and US Fish and Wildlife's 2008 Biological Opinion for X2.

Expectations

Water management agencies comply with State Water Resources Control Board objectives for salinity in the Delta for D-1641 and X2.
Performance Metrics
Monthly electrical conductivity (EC), water temperature, and X2 in the Delta, evaluated annually.

Compliance Rate of Salinity Objectives in the Delta

Click on the points to view the compliance rates (percentage) and if the targets have been met for that station. This performance measure is evaluated annually. Some stations do not have data or did not have compliance values at that time and will appear as blank or at zero percent. (E.g. Station S-21, S-42)

Compliance reports of D-1641 salinity objectives can be viewed at the State Water Board's website. Suisun Marsh Salinity reports can be found on the California Natural Resource Agency data portal.

Next Data Update: The data below will be regularly updated soon after the beginning of the water year in November.

**Station P12: Starting the 2020 water year, exceedance may occur at multiple times between April and August of a water year, but no action may be taken due to several factors. Details explained on the State Water Board's website.

X2 in the Delta

X2 is designed specifically to protect the aquatic life of the Delta estuary. X2 is a physical attribute of the estuary used as a habitat indicator for the location of the low salinity zone. X2 is the location in kilometers from the Golden Gate Bridge where water salinity is 2 ppt (parts per thousand) of isohaline salt. The low salinity zone is where freshwater transitions into brackish water. Historically, the low salinity zone was associated with high primary productivity, zooplankton population, and abundance of native species.

The Fall X2 targets for September and October come from the USFWS Delta Smelt Biological Opinion Fall X2 Action and California Department of Fish and Wildlife's (CDFW) Incidental Take Permit (ITP) to maintain the low salinity habitat at or less than 80 km from the Golden Gate Bridge in the fall following wet and above normal water years.

In 2024, CDFW issued a temporary amendment to the ITP that allowed for no requirement to maintain the monthly average X2 of 80km for the month of October and for alternative implementation of the Summer Fall Action to operate Suisun Marsh Salinity Control Gates daily from September 6 – September 30, 2024

Next Data Update: The data below will be regularly updated soon after the beginning of the water year in wet and above normal water years. California water years run from October 1st to September 30th. Provisional water year designations are available after each water year ends and final water year designations are available later the following year (i.e., 2025).

X2 Locations — Map of Delta and San Francisco Estuary with kilometer ticks illustrating distance from the Golden Gate Bridge

USFWS Biological Opinions and X2

2024 Biological Opinion

In 2024, the USFWS released an updated Biological Opinion (BiOps) on the operation of the CVP and SWP. The 2024 BiOps carries over similar requirements as the 2019 BiOps for X2, requiring the California Department of Water Resources and the Bureau of Reclamation to maintain an average of 80 km or less from the Golden Gate in “above normal” and "wet” years for September through October. It also included other measures, such as the operation of the Suisun Marsh Salinity Control Gates and fish food enhancement actions, that are expected to achieve ecological benefits. Prior to the 2019 BiOps, the X2 target was at 80 km or less following above-normal years and 74 km or less for wet years in September and October.

CDFW ITP

In March 2020, CDFW issued an ITP to the Department of Water Resources for long-term operations of the State Water Project. The ITP covers four protected species under the California Endangered Species Act: Delta Smelt, Longfin Smelt, Winter-run Chinook Salmon, and Spring-run Chinook Salmon. The ITP authorization will expire on March 31, 2030, unless renewed.

About the Measure

Salinity in the Delta is an important water quality characteristic affecting municipal, industrial, agricultural, and fish and wildlife water uses. Changes in Delta salinity have far-reaching impacts, from affecting water supply for farmers in the Central Valley to the wildlife and ecosystems of the San Francisco Bay. When salinity exceeds compliance conditions or changes too rapidly, it can have negative impacts on many beneficial uses of water. This includes altered water taste and availability, crop damage and loss, and limitations for recharging groundwater.

The Delta is a transition zone between freshwater and saltwater, serving as an important habitat for hundreds of native terrestrial and aquatic organisms. The amount of freshwater flowing into and through the Delta drives seasonal and annual salinity levels.

Both natural and man-made actions affect salinity in the Delta and Suisun Marsh. Tidal forces, agricultural run-off, exports, and freshwater inflow from the Sacramento and San Joaquin Rivers jointly influence salinity levels of the Delta. The management of salinity is governed by the Department of Water Resources (DWR) and the U.S. Bureau of Reclamation (USBR) due to their roles in managing reservoirs in the watershed and water exports in the Delta. Since DWR and USBR are water right holders for the State Water Project and Central Valley Project, respectively, they must comply with State Water Board Decision 1641 requirements which help protect water quality in the Delta by setting flow and salinity objectives.

Delta Plan Strategy and Recommendations

Each chapter of the Delta plan includes strategies to achieve the goals of the plan. These strategies are general guidance on achieving the objective laid out in the plan and in the Delta Reform Act of 2009. Associated with these strategies are recommendations. The recommendations describe more specific and implementable actions to support the achievement of Delta Plan strategies. Strategies and recommendations may also have associated performance measures. Delta Plan performance measures track progress in achieving desired outcomes for the Delta Plan. Below are the strategies and recommendations associated with this performance measure.

Delta Plan Strategy

Protect beneficial uses by managing salinity

Delta Plan Recommendations

Refer to Chapter 4's functional flows recommendations

Metric, Baseline, and Target

Metric

Monthly electrical conductivity, water temperature, and X2 in the Delta and Suisun Marsh, evaluated annually.

Baseline

Average monthly electrical conductivity, water temperature, and X2 at SWRCB compliance points from 1995 to 2015.

Target

Water management agencies meet SWRCB salinity objectives for ecosystem purposes at least 99 percent of the time at compliance points
Water management agencies meet all other SWRCB salinity objectives for urban and agricultural beneficial use at least 99 percent of the time at compliance points
Water management agencies maintain average X2 for September and October at or less than 74 km in the fall following wet years and at or less than 81 km in the fall following above normal years. The monthly average X2 must be maintained at or seaward of these values for each individual month and not averaged over the two-month period.

Data Sources, Collection, and Processing

Methods

Delta Compliance reports are available from DWR. These reports point out which stations went over the compliance value and for how long.
The specific locations and objectives are located in SWRCB's Water Quality Control Plan Appendix K
Salinity measurements can also be viewed at DWR's CDEC.

Additional Details regarding X2:

2024

USFWS 2019 BiOp requirements in effect.
In September 2024, CDFW issued a minor amendment to the ITP, which affected the X2 average for October. The amendment allowed an alternative implementation to operate to a monthly average X2 of 80 km in September 2024 and operate the Suisun Marsh Salinity Control Gates (SMSCG) daily from September 6 – September 30, 2024. Additionally, in October 2024 the monthly average X2 of 80 km is not required. The operation of the SMSCG on a daily basis from September 6 – 30, 2024 is expected to provide improved habitat conditions for DS in September 2024 beyond what would have been provided by operating in September to a monthly average X2 of 80 km in the absence of SMSCG operations.

2023: USFWS 2019 BiOp and CDFW 2020 ITP requirements in effect.

2019: USFWS 2019 BiOp requirements in effect.

2017:

From the USFWS memo: Relaxed targets of the 2008 BiOPs were approved by US Fish and Wildlife Service (USFWS). U.S. Bureau of Reclamation operated its facilities to achieve an average X2 distance of no greater than 80 km instead of the 74 km for October 2017.
From the CDFW memo: California Department of Fish and Wildlife (CDFW) determined that the change to the implementation of the fall X2 Action in October 2017 was not consistent with the California Endangered Species Act. The Department of Water Resources committed to keep X2 at 79 km monthly average for October to significantly minimize any short-term habitat effects to Delta smelt.

2011: USFWS 2008 BiOp requirements in effect.