Section 131.3 - Definitions(a)The Act means the Clean Water Act (Pub. L. 92-500 , as amended (33 U.S.C. 1251 et seq.)).(b)Criteria are elements of State water quality standards, expressed as constituent concentrations, levels, or narrative statements, representing a quality of water that supports a particular use. When criteria are met, water quality will generally protect the designated use.(c)Section 304(a) criteria are developed by EPA under authority of section 304(a) of the Act based on the latest scientific information on the relationship that the effect of a constituent concentration has on particular aquatic species and/or human health. This information is issued periodically to the States as guidance for use in developing criteria.(d)Toxic pollutants are those pollutants listed by the Administrator under section 307(a) of the Act.(e)Existing uses are those uses actually attained in the water body on or after November 28, 1975, whether or not they are included in the water quality standards.(f)Designated uses are those uses specified in water quality standards for each water body or segment whether or not they are being attained.(g)Use attainability analysis is a structured scientific assessment of the factors affecting the attainment of the use which may include physical, chemical, biological, and economic factors as described in § 131.10(g) .(h)Water quality limited segment means any segment where it is known that water quality does not meet applicable water quality standards, and/or is not expected to meet applicable water quality standards, even after the application of the technology-based effluent limitations required by sections 301(b) and 306 of the Act.(i)Water quality standards are provisions of State or Federal law which consist of a designated use or uses for the waters of the United States and water quality criteria for such waters based upon such uses. Water quality standards are to protect the public health or welfare, enhance the quality of water and serve the purposes of the Act.(j)States include: The 50 States, the District of Columbia, Guam, the Commonwealth of Puerto Rico, Virgin Islands, American Samoa, the Commonwealth of the Northern Mariana Islands, and Indian Tribes that EPA determines to be eligible for purposes of the water quality standards program.(k)Federal Indian Reservation, Indian Reservation, or Reservation means all land within the limits of any Indian reservation under the jurisdiction of the United States Government, notwithstanding the issuance of any patent, and including rights-of-way running through the reservation."(l)Indian Tribe or Tribe means any Indian Tribe, band, group, or community recognized by the Secretary of the Interior and exercising governmental authority over a Federal Indian reservation.(m)Highest attainable use is the modified aquatic life, wildlife, or recreation use that is both closest to the uses specified in section 101(a)(2) of the Act and attainable, based on the evaluation of the factor(s) in § 131.10(g) that preclude(s) attainment of the use and any other information or analyses that were used to evaluate attainability. There is no required highest attainable use where the State demonstrates the relevant use specified in section 101(a)(2) of the Act and sub-categories of such a use are not attainable.(n)Practicable, in the context of § 131.12(a)(2)(ii) , means technologically possible, able to be put into practice, and economically viable.(o) A water quality standards variance (WQS variance) is a time-limited designated use and criterion for a specific pollutant(s) or water quality parameter(s) that reflect the highest attainable condition during the term of the WQS variance.(p)Pollutant Minimization Program, in the context of § 131.14 , is a structured set of activities to improve processes and pollutant controls that will prevent and reduce pollutant loadings.(q)Non-101(a)(2) use is any use unrelated to the protection and propagation of fish, shellfish, wildlife or recreation in or on the water.(r)Tribal reserved rights, for purposes of this part, are any rights to CWA-protected aquatic and/or aquatic-dependent resources reserved by right holders, either expressly or implicitly, through Federal treaties, statutes, or Executive orders.(s)Right holders, for purposes of this part, are any Federally recognized Tribes holding Tribal reserved rights, regardless of whether the Tribe exercises authority over a Federal Indian reservation.48 FR 51405, Nov. 8, 1983, as amended at 56 FR 64893, Dec. 12, 1991; 59 FR 64344, Dec. 14, 1994; 80 FR 51046 , Aug. 21, 2015