State Water Board reviews draft 2026 303(d) list, debates how to treat degraded benthic communities

The State Water Resources Control Board convened a public workshop on March 18 to receive oral comments on the draft Clean Water Act section 303(d) list in the 2026 California Integrated Report. Anna Maria Saenz, senior environmental scientist in the Division of Water Quality, told the board the draft report compiles more than 1.4 million rows of data, producing over 33,000 lines of evidence and about 15,000 water-quality assessments for 983 water bodies.

Saenz said the 303(d) portion of the Integrated Report is informational and that the state listing policy guides how staff translate narrative objectives into numeric evaluation guidelines for assessments. "The 303(d) list identifies waters that do not meet water quality standards due to specific pollutants," she said, and noted that category 4A, 4B and 5 placements constitute the state's 303(d) list for EPA.

A central focus of the workshop was how to treat degraded benthic macroinvertebrate ("benthic") communities in assessments. For 2026 staff proposed placing water-body/pollutant combinations in Category 5 when (1) benthic community data indicate significant degradation compared to reference sites (commonly using the California Stream Condition Index, CSCI) and (2) there is an associated pollutant impairment that could affect aquatic life. Saenz said regional staff assigned TMDL-priority rankings of high, medium or low for Category 5 listings; most benthic listings were assigned low priority.

Board members and public commenters debated whether those same water bodies should instead remain in Category 3 (insufficient information) while staff and researchers refine evaluation methods. Board member Nicole Morgan and others urged caution about applying a single statewide CSCI threshold (0.79) to highly modified channels and large, diverse watersheds such as the Central Valley. Morgan said she supported the addition of Category 5 priority rankings but asked how new or regionally specific CSCI reference conditions would be applied if peer-reviewed research yields alternate scores.

Saenz and other staff said new peer-reviewed studies — including work by the Central Valley research group (SCORP) and regional analyses — could be incorporated as evaluation guidelines once peer review is complete. "If something was listed before using the 0.79 score and there was a different score, then that potentially could be delisted when we apply the new score," Saenz said.

Several public commenters and stakeholder groups warned that Category 5 placements trigger permit-driven responses that can impose substantial monitoring and management obligations on municipal stormwater and other permittees. Karen Cowan, executive director of the California Stormwater Quality Association (CASQA), told the board that municipal stormwater permits require actions for 303(d)-listed pollutants, and that a Category 5 placement, even at low priority, would prompt immediate permit-related planning such as pollutant reduction plans, inventories, and monitoring.

Representatives of agricultural and wastewater interests echoed the concern that treating CSCI-based benthic listings as Category 5 could shift the burden and expense of additional studies to permittees. Tess Dunham (irrigated lands counsel) and Jared Bosco (California Association of Sanitation Agencies) urged caution and recommended retaining a Category 3 approach while methods and peer-reviewed science mature. Thomas Grofhog (Savicqua) and others asked whether adopting 0.79 as a de facto statewide objective would be realistic for tens of thousands of stream miles and whether the board should clarify policy before broader application.

Staff described additional methodology refinements in the draft: better treatment of water-quality objectives that include a nexus to a controllable source or waste discharge; efforts to document when the commercial-and-sport-fishing (COMM) beneficial use is occurring; and a process to correct erroneous listings tied to units errors (staff reported approximately 23 erroneous listings tied to incorrect specific-conductivity units and said zinc and other pollutants may be affected).

Saenz also described ongoing coordination with the Office of Environmental Health Hazard Assessment (OEHHA) to use Integrated Report data for CalEnviroScreen analyses and to identify pollutant impairments in BIPOC and disadvantaged communities. She said letters were sent to tribal entities explaining how tribal data were considered and when tribal-collected data were assessed for waters that border federally recognized tribal lands.

Board members asked staff to continue consultations with regional boards and EPA, and several board members signaled interest in further briefings before the board considers adoption of a final Integrated Report in early 2026. Saenz said written comments on the draft will be accepted through April 2 and staff will release responses and any recommended revisions before asking the board to consider adoption.

Why it matters: the Integrated Report and the 303(d) list direct when and how TMDLs and other regulatory actions are prioritized to address pollutant impairments. Whether degraded benthic communities are listed as Category 5 (with an associated pollutant) or Category 3 (data watch list) affects permitting obligations for municipal stormwater, industrial and agricultural dischargers, and can influence monitoring and restoration priorities.

Next steps: staff will accept public comment through April 2, complete internal reviews on data-unit errors and duplicate submissions, coordinate with permitting programs to clarify how listings are used in permits, and present the proposed final 2026 Integrated Report to the board for adoption in early 2026.