would otherwise be considered to constitute water pollution. For example, the United States Clean Water Act (CWA) defines "pollution" (i.e., water pollution) very broadly to include any and all "man-made or man-induced alteration of the chemical, physical, biological, and radiological integrity of water." However, the Act defines "pollutants" subject to its control more specifically, as "dredged spoil, solid waste, incinerator residue, filter backwash, sewage, garbage, sewage sludge, munitions, chemical wastes, biological materials, radioactive materials [with certain exceptions], heat, wrecked or discarded equipment, rock, sand, cellar dirt and industrial, municipal, and agricultural waste discharged into water." This definition begins to define both the classes or types of materials (e.g., solid waste) and energies (e.g., heat) that may constitute water pollution, and indicates the moment at which otherwise useful materials may be transformed into pollution for regulatory purposes: when they are "discharged into water," defined elsewhere as "addition" of the material to regulated waters. The CWA definition is excluded for sewage discharged from certain classes of vessels, meaning that a common and important class of water pollution is, by definition, not considered a pollutant for purposes of the United States' primary water quality law. (SeeRegulation of ship pollution in the United States.) Although thermal pollution is subject to regulation under the CWA, definitional questions have resulted in litigation, including whether even water itself may qualify as a "pollutant" (e.g., adding warm water to a stream). The United States Supreme Court addressed these issues in Los Angeles County Flood Control District v. Natural Resources Defense Council, Inc. (2013). Water quality standards Ambient water quality standards Determining appropriate water quality standards generally requires up-to-date scientific data on the health or environmental effects of the pollutant under review through water quality criteria. Water quality criteria includes set indicators that determine if water is no longer safe for human health or wildlife based on scientific data. Scientific data includes measurable factors such as temperature, dissolved oxygen, nutrients, toxic chemicals, pollutants, heavy metals, organic micro pollutants, radioactive substances, and sediments. Water quality criteria may require periodic or continuous monitoring of the water body. Based on the criteria, regulatory decisions on water quality standards may change to also incorporate political considerations, such as the economic costs and benefits of compliance. As an example, the United States employs water quality standards as part of its regulation of surface water quality under the CWA. The national Water Quality Standards (WQS)