Clean Water Act (CWA)

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The Clean Water Act (CWA), encoded in 33 U.S.C. Chapter 26, is a landmark piece of legislation in the field of environmental law designed to prevent and repair water pollution in the United States. The Environmental Protection Agency, authorized by the CWA, uses two methods to protect the quality of water: monitoring water quality standards, and controlling discharge from point sources. 

Water quality standards are jointly regulated by the EPA and by the states. States are required to classify bodies of water by their designated use (swimming, fishing, water supply, navigation, industrial waste disposal, ect.), and must adopt a plan to ensure the water meets the standards for that given use. These plans must then receive the approval of the EPA. Achieving this approval requires that pollution limits are sufficient to ensure the water is of high enough quality for its designated use and that the designated uses will not result in further degradation of waterways.  

Water quality plans are determined by both technology-based limitations (requiring polluters to use the best available technology – BAT), and quality-based standards (by setting Total Maximum Daily Limits - TMDL). These TMDL’s approximate the maximum amount of daily pollution that can be discharged into waterways while still meeting EPA standards. 

If a state fails to create standards that satisfy EPA requirements, the EPA may develop a plan itself and require the state to comply. 

In addition to monitoring water quality standards, the CWA requires the regulation of point sources, or stationary locations that discharge pollution into water. Under CWA §301, discharge of a pollutant from a point source into waters of the United States is illegal without a National Pollution Discharge Elimination System (NPDES) Permit.

"Discharge of a pollutant" is broadly defined and almost anything can be considered a pollutant (sediment that blocks sunlight or water at a warmer temperature). Some things, however, are explicitly not included as pollutants. These include agriculture-related stormwater discharge and non-point source discharges like forestry operations. 

NPDES permits are issued either by the EPA itself or by states who obtain the EPA’s approval and allow parties to discharge some level of pollutants into the water of the United States. These permits include limits on how much pollution can be discharged as well as include provisions for mandatory reporting and monitoring procedures. Additionally, these permits cannot last longer than 5 years, after which the permit holder must apply for renewal. For a full list of which states are authorized to grant NPDES permits, see this map at

As with a lot of environmental law, the Clean Water Act includes a notice and comment system. Under this system, notice is provided to the public before any NPDES permit is issued. If they so desire, the public can then comment on the notice and raise concerns they may have regarding whether the permit should be issued. 

The scope of the CWA is limited to the "navigable waters" of the United States, but this has been broadly defined to include wetlands, or areas that are sometimes dry, sometimes wet as well as areas directly adjacent to navigable waters. That said, the reach of the CWA is not unlimited, and it does not apply to unconnected ponds like an old mining quarry which has since filled with water. 

See also: 33 U.S. Code § 1362 - Definitions

[Last updated in July of 2022 by the Wex Definitions Team]