Water Quality Standards

About Water Quality Standards

Water quality standards are regulations that are designed to protect the surface waters of the State. They contain statements and numeric limits that are adopted through administrative rule-making procedures. The standards set forth the water quality needed to protect the uses of the water, such as swimming, public water supply, and the propagation and growth of aquatic life.

Under the Clean Water Act passed in 1972 by Congress, every state must develop and adopt water quality standards to protect, maintain, and improve the quality of the nation’s surface waters. The goal of the Clean Water Act is to “restore and maintain the chemical, physical, and biological integrity of the Nation’s waters”. The interim goal is to have “water quality which provides for the protection and propagation of fish, shellfish and wildlife, and provides for recreation in and on the water”, wherever attainable.

State and Federal Laws and Regulations

Water quality standards requirements are embodied in both state and federal laws and regulations. State law mandates in Section 49-17-19 the protection of public health and welfare and the present use of waters for public water supplies, propagation of fish and aquatic life and wildlife, recreational purposes, and agricultural, industrial, and other legitimate uses. The adoption of water quality standards is the method of accomplishing the law’s purpose.

Mississippi’s water quality standards regulations are entitled Regulations for Surface Water Quality Criteria for Intrastate, Interstate, and Coastal Waters. This document contains all the water quality standards applicable to the state’s surface waters.

How We Protect Your Waters

Designated Uses / Classifications

Designated uses are those uses specified in water quality standards for each water body or segment whether or not they are being attained. They take into consideration the use and value of water for public water supplies, protection and propagation of aquatic life, recreation in and on the water (such as swimming and boating), and protection of consumers of fish and shellfish. It is important that waters of the state are appropriately classified to ensure that the proper criteria is protecting that waterbody. Mississippi waters are classified into the following uses:

  • Public Water Supply
  • Shellfish Harvesting
  • Recreation
  • Fish and Wildlife
  • Modified Fish and Wildlife
  • Drainage Waters
  • Ephemeral

Attainment of these uses is based on specific numeric and narrative criteria, which are also specified in the water quality standards.

To view the designated uses assigned to a specific waterbody please use the links below to access maps and tables organized by river basin. If the waterbody you are looking for is not listed it is classified as Fish and Wildlife.

Click here for the designated uses of the following streams:

  • Big Black River Basin
  • Coastal Streams
  • North Independent Streams
  • Pascagoula River Basin
  • Pearl River Basin
  • South Independent Streams
  • Tennessee River Basin
  • Tombigbee River Basin
  • Yazoo River Basin


Water Quality Criteria

Water quality criteria can include general narrative statements (narrative criteria) and specific numerical concentrations that are calculated to protect aquatic life and human health (numeric criteria). During each triennial review, the criteria are adjusted as needed to reflect changes in law and science.

Narrative “Free Froms”

Narrative “free froms” are general water quality criteria that apply to all surface waters. These criteria state that all waters shall be free from sludge, floating debris, oil and scum, color and odor producing materials, and substances that are harmful to human, animal, or aquatic life. The standards also read that there shall be “no toxics in toxic amounts,” which provides the regulatory basis for establishment and enforcement of Whole Effluent Toxicity (WET) limitations in NPDES permits.

Numeric Criteria

Numeric criteria are estimations of concentrations of chemicals and degree of aquatic life toxicity allowable in a waterbody without adversely impacting its designated uses. These criterion are expressed in a way to take in account how these chemicals affect organisms in the short term, known as acute criteria, and the long term, known as chronic criteria.

EPA periodically compiles results of toxicity tests in which the sensitivity of aquatic organisms to regulated pollutants is determined. In these studies, fish and benthic macroinvertebrates are exposed to known concentrations of a chemical. The short term (acute) and long term (chronic) effects of the exposure are measured, and the results are used to set water quality criteria protective of the most sensitive of species.

Human health water quality criteria are derived based on studies done on the carcinogenic and neurological effects of chemicals to mammals, such as mice, which are then extrapolated to estimate the potential effects to humans.

Based on these tests, national criteria recommendations and guidelines are published by EPA. Mississippi uses these national criteria recommendations, along with other scientific information, to set appropriate water quality criteria for our surface waters. The latest compilation by EPA can be accessed by clicking here.

Site Specific Criteria

There are certain situations that require site-specific criteria to be established. These instances allow for a more localized approach to addressing water quality to a specific waterbody and any unique circumstances that waterbody may have.

Water quality characteristics such as pH, salinity or hardness are known to have an effect on the toxicity of certain pollutants. Knowing this information, certain formulas can be applied in specific situations to take in account actual in-stream conditions.

Numeric Nutrient Criteria

MDEQ is actively working to develop numeric nutrient criteria for Mississippi’s various waterbody types. MDEQ’s mission is to develop scientifically defensible criteria that are appropriate and protective of Mississippi’s waters. The criteria for each waterbody type will be coordinated with other waterbody types to ensure consistency across the state and protection from downstream impacts. Mississippi’s Nutrient Criteria Development Plan can be read by clicking on the link below.

MS Plan for Nutrient Criteria Development

Antidegradation Provisions

The antidegradation provisions describe the conditions under which water quality may be lowered in surface waters. Designated uses must be maintained and protected, and in no case may waters be degraded below the levels necessary to protect existing uses. Water quality better than that needed to protect designated uses must be maintained unless lower quality is deemed necessary to allow important economic or social development.

In theory, antidegradation protects water quality at three levels or “tiers”.

  • Tier 1 specifies that existing instream water uses and the level of water quality to protect the existing uses shall be maintained and protected. This means that as a minimum, all waters should meet adopted water quality standards.
  • Tier 2 protects water that is better than specified water quality standards. Only in limited circumstances may water quality be lowered in these waters.
  • Tier 3 are exceptional waters where no new, additional, or increased discharge of sewage, industrial wastes, or other pollution are allowed. These waters must be specifically listed in the regulation. To nominate a water for Outstanding National Resource Waters (ONRW) consideration, please follow the ONRW Nomination Guidance below.

ONRW Nomination Guidance

Triennial Review Process

The Clean Water Act requires all states to develop, review, revise, and adopt water quality standards every three years known as the triennial review.  Water quality standards must include three components: the designated uses for the state’s waterbodies, the water quality criteria (narrative or numeric) necessary to protect those uses, and antidegradation provisions to protect water quality.

The current water quality standards were adopted by the Mississippi Commission on Environmental Quality on June 24, 2021 and were approved by the EPA on December 17, 2021. Below is a red-line version that shows what changes were made during the last triennial review.

Interested parties can provide input at any time to the department to be considered in the next triennial review.  When water quality standards revisions are proposed, the public is notified of these revisions via newspapers, mailing lists, and website notifications.  In accordance with federal requirements, a public hearing in Jackson, MS, is held to gather input and comments.  Following consideration of comments and any necessary revisions, the standards are adopted by the Mississippi Commission on Environmental Quality.  After adoption, the document is submitted to EPA for review and approval.  Upon approval by EPA, the Standards become effective and can be implemented in NPDES permits, TMDL’s, and other affected programs. If you would like to provide input for consideration in the next Triennial Review please click below.

To contact staff, click here.

Other Clean Water Act Programs

MDEQ monitors the quality of surface water throughout the state to ensure that designated uses are being protected. Monitoring data and information are used to make water quality assessments. Assessments are general characterizations of water body health. The state’s most comprehensive assessment report is the Federal Clean Water Act Section 305(b) Water Quality Inventory Report. For more information on assessments please visit here.

If a waterbody is determined to not be meeting its designated use and is listed as impaired it is subject to a Total Maximum Daily Load (TMDLs). For information on TMDLs please visit this webpage.

Water quality standards apply to ambient waters, as opposed to discharges. These ambient standards form the basis of water quality based permit limitations that regulate the discharge of pollutants into surface waters under the National Pollutant Discharge Elimination System (NPDES) permit program. The NPDES permit regulations are one of the implementation tools of the water quality standards.

Additionally, the standards do not apply directly to municipal drinking water supplies. Drinking water treatment and distribution is regulated by the Mississippi Department of Health, Water Supply Division.

Public Participation

We want to encourage participation and dialogue with interested parties and stakeholders. Staff are happy to provide anybody with information or answer any questions that someone may have. Anyone  can provide input at any time to the department to be considered in the next triennial review. Contact Information can be found here:

Kim Caviness

Patrick Felch