Water Quality Assessment

Integrated Report – 303(d) list of water quality limited segments and 305(b) surface water quality assessments

Clean Water Act (CWA) Section 303(d) requires states to identify waterbodies that do not meet water quality standards. Waterbodies which do not meet water quality standards are placed on the CWA Section 303(d) List of Water Quality Limited Segments (also known as the list of impaired waterbodies, or the 303(d) list).

The 303(d) list identifies the pollutant(s) or stressor(s) causing impairment(s) and establishes a schedule for developing a water pollution control plan to restore and maintain water quality. In most cases, water quality impairments are addressed by development of a Total Maximum Daily Load (TMDL), although in some cases other regulatory programs will address the impairment instead of a TMDL. Adoption and implementation of a TMDL or alternative regulatory program serves to attain and maintain water quality standards for the impaired waterbody.

CWA section 305(b) requires States to prepare and submit to USEPA a report on the overall water quality conditions for all navigable water bodies in the State. California develops an Integrated Report to satisfy the requirements of CWA Sections 303(d) and 305(b).

California’s Integrated Report is developed in "cycles" with each cycle occurring every two years. Each Integrated Report cycle consists primarily of assessments from three Regional Water Quality Control Boards. The other six Regional Water Quality Control Boards that are "off-cycle" may also assess new high-priority data and make new listing or delisting decisions for one or more waterbodies. The most recent Integrated Report cycle for the Lahontan Region was the 2018 Integrated Report.

Lahontan Region waters are being assessed in the 2026 Integrated Report. Since the 2020-2022 California Integrated Report cycle, the State Water Board has been administering the public process, including board hearings and development of the integrated report. While the Regional Water Boards play a significant role in the development of the integrated report, the Regional Water Boards no longer conduct individual board hearings and public comment periods. The State Water Board's Surface Water Quality Assessment program website contains all the public documents for the development of the 2026 Integrated Report.

If you would like to receive announcements and notices pertaining to the Integrated Report for the Lahontan Region by e-mail, please visit our e-mail subscriptions page and subscribe to the “303(d) List – Impaired Waters” list. You can also subscribe to the State Water Board’s “Integrated Report 303(d)/305(b)” email subscription list at the State Water Board’s email subscription page under Water Quality to receive announcements and notices pertaining to the statewide Integrated Reports.

California Integrated Report Fact Sheet

• California Integrated Report Fact Sheet

2026 California Integrated Report (in development)

• 2026 California Integrated Report (in development)

2024 Integrated Report and 303(d) List

• 2024 Integrated Report and 303(d) List– the current, fully approved California Integrated Report

Previous Integrated Reports

2018 Integrated Report

• 2018 Integrated Report and 303(d) List
• On November 20th, 2019 the Lahontan Water Board adopted Resolution R6T-2019-0276 to transmit the regions' recommended updates to the 303(d) List to the State Water Board.
• On October 20, 2021, the State Water Board approved the 2018 California Integrated Report, which included updates to the 303(d) List for the Lahontan Region.
• On June 9, 2021, U.S. EPA approved the 2018 California Integrated Report. Signed Resolution R6T-2019-0276 and Enclosure 1
• Lahontan Region 2018 Integrated Report Transmittal Letter to the State Water Board
• Response to Public Comments
• Final Staff Report
  • Final Appendix A - Proposed Updates to the 303(d) List
  • Final Appendix B - Category 5 Waterbody Segments
  • Final Appendix C - Category 4a Waterbody Segments
  • Final Appendix D - Category 4b Waterbody Segments
  • Final Appendix E - Category 3 Waterbody Segments
  • Final Appendix F - Category 2 Waterbody Segments
  • Final Appendix G - Category 1 Waterbody Segments
  • Final Appendix H - Waterbody Fact Sheets
  • Final Appendix I - Decisions affected by the re-segmentation of the Susan River and West Fork Carson River
  • Final Appendix J - Reference Report for Fact Sheets
• Lahontan Region 2018 Integrated Report Map

2012 Integrated Report

• Statewide 2012 Integrated Report (CWA Section 303(d) List / 305(b) Report)
• Lahontan Region 2012 Integrated Report
• U.S. EPA final approval letter and addition of Topaz Lake

Historical California Integrated Reports, 303(d)Lists, and 305(b) Reports

• Historical California Integrated Reports, 303(d)Lists, and 305(b) Reports