The 303(d) List of Impaired Water Bodies

For 303(d), State and Regional Water Boards assess water quality monitoring data for California’s surface waters every two years to determine if they contain pollutants at levels that exceed protective water quality standards. Every two years, the integrated report reflects the analyses of all available
data and information from surface waters within the boundaries of three Regional Water Boards, which are referred to as being “on-cycle”. Data from the rest of the state may be reviewed for “off-cycle”  assessments. Every region is “on-cycle” and fully assessed once every six years.

Water bodies and pollutants that exceed protective water quality standards are placed on the State’s 303(d) List. In California, this determination is 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. Placement of a water body and pollutant on the 303(d) List requires the development of a Total Maximum Daily Load (TMDL), a water quality improvement plan. In some cases, other regulatory programs will address the impairment instead of a TMDL, or the water quality may improve as a result of remedial actions or implementation of control measures.

CWA Section 305(b) requires each State to report biennially to U.S.EPA, on the condition of its surface water quality. For the 305(b) Report, State and Regional Water Boards place the water body segments that were assessed into one of U.S.EPA’s five Integrated Report beneficial use report categories. These reports are combined in a report called the California 303(d)/305(b) Integrated Report.California has been developing 303(d)/305(b) Integrated Reports every two years since 1976, and these reports are available in electronic format on the State Board's Water Quality Assessment web page.

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. All public documents are available on the State Board's program page.