The Clean Water Act (CWA) prohibits "the discharge of any pollutant" into waters of the United States, except as otherwise authorized under the Act. A "discharge of a pollutant" is defined as "any addition of any pollutant to navigable waters from any point source." The national pollutant discharge elimination system (NPDES) permit program regulates point source discharges of pollutants into waters of the United States. The issue of whether water transfers are subject to NPDES permit requirements has been surrounded by considerable controversy. The question is of particular concern to the water supply and user communities because transbasin transfers of water from one water body to another for municipal, agricultural, and commercial purposes, among other activities, are essential for meeting those needs.

The U.S. Environmental Protection Agency (EPA) first addressed this issue in 1975 with an interpretation stating that an NPDES permit was required when irrigation ditches discharge into navigable water, even if the irrigation ditches also qualify as navigable waters. The opinion was based on EPA's interpretation of the plain meaning and legislative intent of the CWA. However, that opinion dealt with a narrow issue and did not address transfers that merely convey navigable waters. The opinion also stated that to the extent the opinion could be interpreted to apply more broadly to water transfers, it was superseded by EPA's subsequent interpretations specifically addressing such transfers.