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Water: Animal Feeding Operations

Animal Feeding Operations Overview


Animal Feeding Operations (AFOs) are agricultural operations where animals are kept and raised in confined situations. AFOs generally congregate animals, feed, manure, dead animals, and production operations on a small land area. Feed is brought to the animals rather than the animals grazing or otherwise seeking feed in pastures. Animal waste and wastewater can enter water bodies from spills or breaks of waste storage structures (due to accidents or excessive rain), and non-agricultural application of manure to crop land.

cafo collage

An AFO is a lot or facility (other than an aquatic animal production facility) where the following conditions are met:

  • Animals have been, are, or will be stabled or confined and fed or maintained for a total of 45 days or more in any 12-month period, and
  • Crops, vegetation, forage growth, or post-harvest residues are not sustained in the normal growing season over any portion of the lot or facility.

AFOs that meet the regulatory definition of a concentrated animal feeding operation (CAFO) may be regulated under the NPDES permitting program. The NPDES program regulates the discharge of pollutants from point sources to waters of the United States. CAFOs are point sources, as defined by the CWA [Section 502(14)]. To be considered a CAFO, a facility must first be defined as an AFO.

Previous EPA regulations based the definition of CAFOs on the number of "animal units" confined. EPA no longer uses the term "animal unit," but instead refers to the actual number of animals at the operation to define a CAFO. Click here to view a brief summary of how the regulations define Large, Medium, and Small CAFOs (PDF) (1 pg, 21K, About PDF).


Click on the links below to find out more information and facts on AFOs, CAFOs, and the NPDES permitting program for CAFOs.

  • CAFO Final Rule - Provides information about the 2003 and 2008 Final CAFO Rules including the preamble and regulatory text for both final rules.
  • CAFO Rule History - Outlines the history and regulatory actions leading to the current final rule and provides links to historical rule documents.
  • General Information - Provides links to guidance documents, information on funding sources for AFOs, and other important AFO/CAFO information.

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