Total Maximum Daily Loads (TMDLs)

What are TMDLs?

A Total Maximum Daily Load (or TMDL) is the amount of a specific pollutant - such as trash, bacteria or pesticides - that is allowed in specific water bodies like rivers, creeks, lakes or the ocean. State and federal laws require the City of Los Angeles to comply with multiple TMDLs in all four of Los Angeles watersheds to protect the quality of our region’s water resources.

The Los Angeles Water Resources Control Board is responsible for establishing water quality standards in the Los Angeles area and these standards are described in the Los Angeles Water Quality Control Plan (or Basin Plan). The Resources Control Board places all bodies of water that do not meet water quality standards on a list of “impaired” waters and this list is re-evaluated every two years.

How are TMDLs Developed?

Once a body of water is declared impaired, the Los Angeles State Resources Control Board determines the priority and schedule for the development of TMDLs, which includes the following key steps:

  • Examine pollutant-specific water quality issues
  • Identify the sources of pollution
  • Define how much of a pollutant a body of water can receive and still meet the water quality standards
  • Allocate pollutant loads (“total maximum daily loads”) to each identified pollutant source
  • Development implementation plans to achieve TMDL targets and compliance
  • Monitor and evaluate water quality to determine success

The City of Los Angeles, through a collaborative stakeholder process that includes community groups, environmental organizations and regulatory agencies is committed to working on developing implementation plans that will improve Los Angeles water quality and ensure compliance with TMDL regulations.

You may also want to download the What are TMDLs? Fact Sheet for print ready information.