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Water Quality Standards 

The objective of the Clean Water Act of 1972 along with its amendments are to restore and maintain the chemical, physical, and biological integrity of the nation’s waters. The first national set of water quality standards were published in 1983 and codified in 40 CFR Part 131. These regulations allow individual states to construct their own water quality standards framework providing there is no reduction in protection compared to federal guidelines.

Missouri’s Water Quality Standards are reviewed and modified every three years. Termed the triennial review process, coordinators with the Missouri Department of Natural Resources meet with the U.S. Environmental Protection Agency, other state agencies, and concerned citizens to evaluate the effectiveness of our standards. Visit the Water Protection Program Rule Development page for up-to-date information on the status of 10 CSR 20-7.031-Water Quality Standards rule. Discussions of Water Quality Standards topics are being conducted through the Water Protection Forum, Water Quality Standards Workgroup.

Water quality standards provide a means by which attainment of water quality objectives can be measured. The objective is protection of designated uses through the application of narrative or numeric criteria. The level of protection given to a stream, lake, or river is dependent on the expected or "designated use(s)," of that water. Classified waters in Missouri have been assigned the designated uses that are listed in 10CSR 20-7.031(C) page 10. The antidegradation section requires actions to maintain existing uses. Attainment frequency of water quality standards are used in identifying and characterizing waters of the state for purposes of compiling the 303(d) list and 305(b) report. In addition, effluent limits contained in National Pollution Discharge Elimination System (NPDES) permits are frequently derived using water quality standards.

UPDATE: The EPA approved Missouri's Numeric Nutrient Criteria (NNC) for lakes and reservoirs on Dec. 14, 2018. The NNC approved by EPA address EPA's 2011 disapproval of NNC previously promulgated by the state. The EPA will continue to review the other components of the April 13, 2018 Water Quality Standards submittal and will act on those revisions at a later date. A link to the approval letter and decision document are provided below under EPA Actions on Water Quality Standards.

Evaluation of Environmental and Economic Impacts of Revised Water Quality Standards and Criteria on a Subbasin Basis
Section 644.058 of the Missouri Revised Statutes requires and evaluation of environmental and economic impacts be made when criteria are revised more than 25%.

Missouri Initiates Development of Nutrient Criteria For Water Quality

Water Quality Standards Map Viewer

Water Protection Rule Development

Recreational Use Attainability Analysis

Presumed Use Reviews

EPA’s Water Quality Standards

Wetland Water Quality Standards

EPA Actions on Water Quality Standards