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Clean Water Act and TMDLs explained

January 03, 2002

Congress enacted the Clean Water Act in 1972. The act deals with water quality issues in water bodies generated from "point sources" and "nonpoint sources."

Section 303(d) of the law requires states to identify all water bodies (lakes, rivers, and other water bodies like agricultural drains) that do not meet applicable water quality standards (impaired water bodies).

Once water bodies are identified, states must establish total maximum daily loads that define how much of a "pollutant" a water body can tolerate on a daily basis and still meet water quality standards that are set for a particular water body.

This section of the CWA was ignored for many years. However, environmental lawsuits and court orders breathed new life into the requirements of this section.


In California, there are more than 500 water bodies on the 303(d) list. Regional Water Quality Control boards are responsible for establishing and implementing the TMDLs. Section 303(d) requires California Regional Water Quality Control boards to identify water bodies that do not comply with the applicable water quality standards.

The boards then are expected to rank the impaired water bodies, taking into account the severity of the pollution and the beneficial uses of such waters.

Regional boards also are expected to establish TMDLs for the identified pollutants and set limits for these pollutants such that these water bodies attain their beneficial uses.

A list of impaired water bodies in the Salton Sea watershed is available on the Web site of the state Colorado River Basin Region (

The list in that region includes bodies of water like the Alamo River, New River, Imperial Valley agricultural drains, Salton Sea and Coachella Valley storm water channel. According to the list, major "pollutants" impairing these waters are silt, pesticides, salts, nutrients (fertilizers) and other pollutants.

The regional board has already established a draft of the sedimentation/siltation TMDL for the Alamo River and a draft pathogen TMDL for the New River.

The CRWQCB is in the process of establishing the Salton Sea nutrient TMDL. The process will take about three years and likely will establish guidelines for the nutrient TMDL that will improve water quality in the region.

Complying with TMDL standards will add an additional financial burden on growers in the Imperial Valley.

Agricultural drains and rivers in the Imperial Valley provide excellent habitat for wildlife. Alfalfa and many other crops are grown in the Imperial Valley solve pollution problems. For example alfalfa, the dominant crop in the Valley, is grown on more than 1 million acres in California and has been used to mitigate environmental problems. Alfalfa fields in California are used to recycle dairy and municipal wastes. For additional information about the impact of alfalfa on the environment visit our alfalfa Web site ( and click on Alfalfa Queen of Forages: Enhancing Wildlife and Protecting our Soil.

Sources: EPA ( and California SWRCB (

>> Khaled M. Bali is the irrigation/water management adviser at the University of California-Imperial County Cooperative Extension.

>>The Cooperative Extension serves all residents of the Imperial Valley.

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