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Water Quality Assessment

Lahontan Region 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). Decisions to place waterbodies on the 303(d) list are governed by the Water Quality Control Policy for developing California’s Clean Water Act Section 303(d) List. U.S. EPA must approve the 303(d) list before it is considered final.

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 which satisfies 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 the 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 will next be assessed in the 2026 Integrated Report, currently under development.

To learn more about the Integrated Report evaluation process, please visit the State Water Board's Surface Water Quality Assessment website

If you would like to receive announcements and notices pertaining to the Integrated Report by e-mail, please visit our e-mail subscriptions page.

2026 Integrated Report (in development)

Data solicitation notice for the 2026 Integrated Report. The solicitation period closes October 21,2022. Data submitted after the solicitation closure will not be assessed in the 2026 Integrated Report Cycle.

2020-2022 Integrated Report and 303(d) List

2018 Integrated Report

2012 Integrated Report

2010 Integrated Report

Previous 303(d) lists and 305(b) reports

The 2010 Integrated Report is the first Integrated Report developed for the State of California. Previous assessments were developed by the State Water Board in separate documents and can be found on the State Water Board’s Integrated Report Cycles website.