Front-line responsibility for protecting California’s water quality and policing waste discharges in the state rests primarily with nine regional water quality control boards overseeing water quality in major watersheds from Oregon to Mexico.

The nine regional boards are semi-autonomous from the State Water Resources Control Board, which is charged with allocating surface water rights and setting statewide policy on water quality. The regional boards are comprised of seven part-time board members appointed by the Governor and confirmed by the state 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.

BACKGROUND

World War II brought rapid industrial development and population growth to California, and with them came water pollution and water-borne disease outbreaks. Attempts to regulate the sources of water pollution were complicated by conflicting interpretations of existing laws and overlapping authority among government agencies.

In an attempt to better address California’s water pollution concerns, the state Legislature in 1949 passed the Dickey Water Pollution Act. Authored by Randal F. Dickey, a Republican assemblyman from the city of Alameda, the act created a State Water Pollution Control Board to oversee statewide water pollution policy, and regional water pollution control boards to be the enforcing agency in each of the state’s nine major watersheds.

Over the next two decades, new legislation would rename the state and regional water boards, expand the state board’s duties to include surface water rights, and – with the enactment in 1969 of the Porter-Cologne Water Quality Control Act – strengthen the state’s oversight of water quality affecting beneficial uses of surface and groundwater. The Porter-Cologne Water Quality Control Act – coauthored by Sen. Gordon Cologne, a Riverside County Republican, and Assemblyman Carley Porter, a Los Angeles County Democrat – became the model for the federal Clean Water Act in 1972.

Below are the nine regional water quality control boards and the counties they cover.

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.

Updated December 2025.