Delta Water Quality

Outcome Performance Measure 6.1, Last updated: January 17, 2023 | About this Measure
The 2020-2022 update to the 303(d) list shows a 30% net increase of waterbody-contaminant combinations in the Delta and Suisun Marsh since the 2014-16 update.

The Measure

Water quality in the Delta and Suisun Marsh meets the standards of the Clean Water Act.

  • Expectations

    Reduction of Delta waterbodies on the 303(d) list to achieve the protection of beneficial uses in the Delta.

  • Performance Metrics

    The number of Delta watershed waterbody contaminant combinations on the 303(d) list, evaluated every eight years.

Waterbody-Contaminant Combinations in the Delta and Suisun Marsh

The bar graph below shows the total number of waterbody-contaminant combinations in the Delta and Suisun Marsh for each 303(d)-list update. The new waterbody-contaminant combinations added to the 303(d)-list from the most recent update (2020-22) included major pollutants such as pesticides (36% of new listings), total dissolved solids (16%), nutrients (16%), other (14%), and metals (8%). The number of Delta and Suisun Marsh waterbody contaminant-combinations should be less than 40 percent of the 2010 baseline values by 2034, marked as a dotted line on the graph.

The 303(d) List

The full list of impaired waterbodies on the 303(d) list can be downloaded and viewed as a map through the State Water Board website.

2020-22 Impaired Water Bodies

2020-2022 Impaired Delta and Suisun Waterbodies

This table is a list of Delta and Suisun Marsh Waterbody-Contaminant Combinations that are listed in the 303(d) list.

Next Data Update: Data will be updated soon after the approval of the integrated report by the United States Environmental Protection Agency. The next full assessment update of the 303(d) integrated report for the Central Valley will be in 2028.

Consistent good water quality is crucial for successful restoration efforts of aquatic habitats and other beneficial uses of Delta water. High amounts of pollutants, or other water quality issues, can impair the ability of water to support beneficial uses, such as: recreational use, agricultural water supply, municipal water supply, and healthy habitat for native vegetation and wildlife. Reduction of impaired water bodies on the 303(d) list of the Clean Water Act is important for the protection of beneficial uses in the Delta.

The Clean Water Act (CWA) protects and restores surface water quality by regulating pollutants and quality standards for the waters of the United States. The State Water Quality Control Board (SWRCB) and its regional boards evaluate surface water quality data and develop a list of waters that do not meet established water quality standards (impaired waters) and those that currently meet water quality standards but may exceed it in the next reporting cycle (threatened waters).

Clean Water Act

The 303(d) list contains the waterbody name and the type of contaminant in the waterbody. A waterbody can contain several combinations of contaminants. The 303(d) list is evaluated every two years to determine if waterbodies meet the water quality standards. Polluted waters continue to be monitored and assessed until applicable water quality standards are met. The SWRCB issues integrated reports with updated 303(d) water bodies list.

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

  • Require Delta-specific water quality protection

Delta Plan Recommendations

  • Protect beneficial uses
  • Identify covered action impact
  • Special water quality protections for the Delta
Metric
  • The number of Delta watershed “waterbody-contaminant” combinations on the 303(d) list, evaluated every eight years within the State Water Resources Control Board (SWRCB) Integrated Report
Baseline
  • Measured as of the 2010 SWRCB Integrated Report
Target
  • Reduction of 40 percent of the “waterbody-contaminant” combinations on the 303(d) list by 2034
Methods

Impaired waterbodies are listed (303(d) List) in the State Water Resources Control Board's Integrated report.

  1. We downloaded the 303d list and the accompanying GIS file.
  2. Then used ArcGIS (10.4) to clip the 303d list within the boundaries of the Delta and Suisun Marsh and summed the number of waterbody-contaminant combinations in the list.
  3. Then compared it to the previous integrated report (baseline).

Example of waterbody-contaminant combination: Water Body Name paired with the type of pollutant. A waterbody can be listed more than once if it contains several pollutants.

Data Source
2010 Integrated Report
2016 Integrated Report

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