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Water Quality

Nonpoint Source Water Pollution

Nonpoint source (NPS) water pollution does not come from a single, identifiable source but from a wide variety of diffuse sources which are often difficult to identify, isolate and control. Most NPS pollution enters our rivers, streams, lakes, wetlands and coastal waters through surface water runoff. Agriculture is a significant source of surface and groundwater NPS pollution in California. Livestock operations can contribute sediment as well as a variety of pollutants associated with animal waste, including bacteria and nutrients like phosphorus and nitrogen. Potential NPS pollutants associated with irrigated agriculture include sediment, nutrients, pesticides, salinity, pathogens, and trace elements. For additional information on how livestock and agricultural operations contribute to NPS pollution, see the following UC Agriculture and Natural Resources (ANR) reference sheets:

Water Quality Regulation

The State Water Resources Control Board and Regional Water Quality Control Boards (locally, the North Coast Regional Water Quality Control Board and San Francisco Bay Regional Water Quality Control Board) are responsible for enforcing all state and federal laws and regulations pertaining to water quality. This includes the Clean Water Act and California's Porter-Cologne Act. All state and federal water quality laws and regulations are summarized in the ANR publication Water Pollution Control Legislation, and more detailed information is available on the Laws/Regulations page of the State Water Resources Control Board website. The responsibilities of agriculturists and natural resource managers with regard to water quality regulation compliance in California are outlined in the ANR publication State and Federal Approach to Control of Nonpoint Sources of Pollution.

The authority to protect water resources statewide requires the Regional Boards to address both point and nonpoint sources of pollution affecting groundwater and surface water, including coastal waters. Regional Boards have the authority to issue the following permits and restrictions:

  • Waste Discharge Requirements (WDR) are essentially permits with specific conditions that define where, when and how discharges to water bodies are allowed. They require annual fees and approval by the Board and are the most restrictive and expensive type of permits.
  • Waivers of WDR are also conditional permits to discharge pollutants, but they typically have lower annual fees and do not require approval by the Board.
  • Basin Plan Prohibitions are restrictions on pollutant discharges contained within a Region's Basin Plan, rather than issued to individuals or groups as a permit. This tool is used when discharges are occurring without either of the first two types of permits, providing for immediate enforcement action to control a discharge.

Basin Plans

One of the most important functions of the Regional Boards is to draft, and periodically update, water quality control plans, or Basin Plans, for the watersheds in their regions. Basin Plans establish beneficial uses of water for each water body, specific water quality standards for surface and ground water, and the actions necessary to control point and nonpoint sources of water pollution. In short, Basin Plans provide a definitive program for preserving and enhancing water quality and protecting beneficial uses of water. All permits issued to control pollution within California must implement Basin Plan requirements.

Total Maximum Daily Loads

Total Maximum Daily Loads (TMDLs) are used by the Regional Boards and the US Environmental Protection Agency to identify watersheds with impaired beneficial uses and develop plans to mitigate impairments. The definition of a TMDL is the "sum of the individual wasteload allocations for point sources, load allocations for nonpoint sources and natural background pollutants, and an appropriate margin of safety (USEPA)." Resource and regulatory agency staff use the term TMDL to refer to a definition, a process, and a document. As a process, TMDLs serve to identify impaired water bodies and contributing sources of pollution, and to define mitigation measures to address those sources and remove impairments. Upon completion of the technical TMDL, the State is charged with ensuring that the necessary mitigation measures are implemented.

The following publications discuss the history of TMDLs, the politics and controversy surrounding them, and the implications of TMDLs for water quality and pollution control:

Water bodies scheduled to have TMDLs developed are listed on the California 303(d) List and TMDL Priority Schedule. This list is updated and revised every two years. To learn the TMDL status of a specific water body, check SWRCB's statewide 303(d) list. Additional information about TMDLs is provided by:

University of California Water Quality Resources

Additional Water Quality Resources and Information