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…