There are nine regional water quality control boards statewide.

The nine Regional Boards are semi-autonomous and are comprised of seven part-time Board members appointed by the Governor and confirmed by the Senate. Regional boundaries are based on watersheds and water quality requirements are based on the unique differences in climate, topography, geology and hydrology for each watershed. Each Regional Board makes critical water quality decisions for its region, including setting standards, issuing waste discharge requirements, determining compliance with those requirements, and taking appropriate enforcement actions.

Region 1 — North Coastal Regional Water Quality Control Board
Del Norte, Glenn, Humboldt, Lake, Marin, Mendocino, Modoc, Siskiyou, Sonoma, and Trinity counties.

Region 2 — San Francisco Regional Water Quality Control Board
Alameda, Contra Costa, San Francisco, Santa Clara (north of Morgan Hill), San Mateo, Marin, Sonoma, Napa, Solano counties.

Region 3 — Central Coastal Regional Water Quality Control Board
Santa Clara (south of Morgan Hill), San Mateo (southern portion), Santa Cruz, San Benito, Monterey, Kern (small portions), San Luis Obispo, Santa Barbara, Ventura (northern portion) counties.

Region 4 — Los Angeles Regional Water Quality Control Board
Los Angeles, Ventura counties, (small portions of Kern and Santa Barbara counties).

Region 5 — Central Valley Regional Water Quality Control Board
Modoc, Shasta, Lassen, Plumas, Butte, Glen, Colusa, Lake, Sutter, Yuba, Sierra, Nevada, Placer, Yolo, Napa, (N. East), Solano (West), Sacramento, El Dorado, Amador, Calaveras, San Joaquin, Contra Costa (East), Stanislaus, Tuolumne, Merced,Mariposa, Madera, Kings, Fresno, Tulare, Kern. (Very small portions of San Benito, San Luis Obispo) counties.

Fresno Office: Fresno, Kern, Kings, Madera, Mariposa, Merced, and Tulare counties. Redding Office: Butte, Glen, Lassen, Modoc, Plumas, Shasta, Siskiyou, and Tehama Counties.

Region 6 — Lahontan Regional Water Quality Control Board
Modoc (East), Lassen (East side and Eagle Lake), Sierra, Nevada, Placer, El Dorado, Alpine, Mono, Inyo, Kern (East), San Bernardino, Los Angeles (N/E corner) counties.

Region 7 — Colorado River Regional Water Quality Control Board
Imperial, San Bernardino, Riverside, San Diego counties.

Region 8 — Santa Ana Regional Water Quality Control Board
Orange, Riverside, San Bernardino counties.

Region 9 — San Diego Regional Water Quality Control Board
San Diego, Imperial, Riverside counties.