Water flowing in a stream

Missouri’s Water Quality Standards (WQS), which are defined in Code of State Regulations 10 CSR 20-7.031, describe the desired condition of a body of water and the means by which that condition will be protected or achieved. There are flexibilities built into the WQS, which allow for periodic review and revision of uses, time-limited alteration of criteria, and consideration of site-specific conditions during criteria development. Missouri Revised Statutes section 644.058, RSMo. requires an evaluation of environmental and economic impacts be made when criteria are revised more than 25%.

The water quality standards in state regulations describe the desired condition of a body of water and the means by which that condition will be protected or achieved. The department uses water quality testing parameters to determine the water quality in Missouri. A variance to the water quality standards is possible to allow deviation from meeting a water quality-based effluent limit for dischargers. For more information about variances or a list of variances in process, visit Water Quality Standards Variances.

We can help you with these technical issues. Email us at wqs@dnr.mo.gov

Site-Specific Criteria

Water quality criteria are typically developed to be protective of Missouri's waters on a statewide level. This means we have to make certain assumptions about local water quality conditions where data is not available. However, Missouri's Water Quality Standards (WQS) allow for a petitioner to request site-specific criteria, located in 10 CSR 20-7.031(5)(S). The petitioner must provide us with sufficient documentation to show the current criteria are not adequate and the proposed site-specific criteria will protect all uses of the water body.

Please contact us at wqs@dnr.mo.gov if you wish to develop site-specific criteria or if you would like additional information on the topic. Early coordination will ensure the use of quality data, proper analysis and defendable procedures.

Site-specific Dissolved Oxygen Criteria for Sni-A-Bar Creek


Numeric Nutrient Criteria

Use Attainability Analysis

Use Attainability Analyses (UAAs) are the means we use to determine whether designated uses are existing or attainable on Missouri’s waters. A designated use may be removed if attaining the use is not feasible because of one of these six factors:

  1. Naturally occurring pollutant concentrations
  2. Natural, ephemeral, intermittent, or low flow conditions
  3. Human caused conditions cannot be remedied or would cause more environmental damage to correct than to leave in place
  4. Dams, diversions, or other hydrologic modifications
  5. Physical conditions related to natural features preclude aquatic life uses
  6. Controls more stringent than needed to meet technology-based limits cause substantial and widespread economic and social impact

Missouri’s Water Quality Standards (WQS) outline the basic requirements for making a use attainability demonstration, located in 10 CSR 20-7-031(2)(F). Additionally, the department developed the Missouri Recreational Use Attainability Analyses: Water Body Survey and Assessment Protocol for conducting a UAA for recreational uses.

Proposed Recreational Use Removals - 2020 Triennial Review

Presumed Use Review

On Oct. 22, 2014, the U.S. Environmental Protection Agency approved Missouri’s Water Quality Standards regulation incorporating the Missouri Use Designation Dataset (MUDD), which increased the total miles of streams with “fishable/swimmable” uses from 24,482 miles to 115,772 miles. The MUDD assigned these newly “classified” streams with the following presumed uses:

  • Aquatic habitat protection
  • Human health protection
  • Whole body contact recreation – Category B
  • Secondary contact recreation
  • Livestock and wildlife protection
  • Irrigation

However, presumed uses shall not apply to water bodies that meet one of the following criteria:

  • Waste treatment systems, or prior converted cropland
  • Man-made structures which were constructed solely to treat or convey wastewater
  • Man-made bodies of water or structures which lack perennial flow and were constructed to treat, convey, or temporarily hold or slow stormwater following precipitation events
  • Water bodies that lack jurisdiction under either the federal Clean Water Act or Missouri Clean Water Law

With reasonable evidence, we will make a written determination regarding the applicability of a water body’s presumed uses. The written determination is subject to appeal pursuant to section 621.250, RSMo. If it is determined that the presumed uses should not apply to the water body in question, we will update the MUDD through a Water Quality Standards rulemaking.

Presumed Use Reviews In Process

We have reviewed presumed use applicability on water bodies for the following permittees. We will incorporate any use changes as a result of these reviews into the current Water Quality Standards rulemaking.