Maryland's Surface Water Quality Standards


Maryland's 2023 Interim Update to Water Quality Standards​

MDE proposed several minor corrections to COMAR  A notice of final action for the 2023 Interim Update was published in the January 26, 2024 issue of the Maryland Register and EPA approved of Maryland's water quality standards changes on May 16, 2024.

More information on the regulatory changes can be accessed here.​

May 17, 2024


What are water quality standards?

The purpose of water quality standards is to protect, maintain and improve the quality of Maryland surface waters. The following make up the three components of water quality standards:
  • Designated Uses,
  • Water quality criteria, and
  • Antidegradation policy.​

What are Designated Uses?

A designated use is a goal for water quality. Typically, the goal is the description of an appropriate intended use by humans and/or aquatic life for a water body. Designated uses for a particular waterbody may include recreation, shellfishing, water supply and/or aquatic life habitat. The designated uses established may or may not be met currently, but must be attainable. In Maryland these designated uses are grouped into "Use Classes" (e.g. Use Class I, I-P, II, III, IV-P) so as to describe a unique combination of designated uses that apply to a single water body. Each stream segment, lake, bay, etc. in Maryland is assigned to a use class.

For more detailed information about Maryland’s designated uses and use class groupings, please click HERE. To go directly to maps of surface waters and their associated use classes, please click HERE.​

What are Water Quality Criteria?

Water quality criteria are expressions of the quality of water as a concentration, level, or narrative statement that, if met, will generally protect a particular designated use.  Maryland has many numeric criteria for protecting aquatic life and human health including for toxics (e.g., lead), physical characteristics of water (e.g., temperature, dissolved oxygen), bacteriological indicators, and even biological endpoints (e.g., quantity of submerged aquatic vegetation). Where s​pecific numeric criteria are not available (e.g., oil, grease, odor, nuisance), narrative criteria apply.​

The Numerical Criteria for Toxic Substances in Surface Waters are provided in the Code of Maryland Regulations (COMAR) Section They can be accessed through the web at:​.

Water Quality Criteria Specific to Designated Uses are provided in COMAR Section T​hey can be accessed through the web at:​.​

What is the Antidegradation Policy?

Maryland’s antidegradation policy and implementation procedures, consistent with the Clean Water Act, provides a framework for maintaining and protecting water quality that has already been achieved. Maryland’s Antidegradation regulations provide for three tiers of protection:

  • Tier I specifies the m​inimum protection standard that must be met—The maintenance and protection of existing and designated uses. This includes support of balanced indigenous wildlife populations and support of contact recreation which is often referred to as "fishable-swimmable."
  • The Tier II antidegradation policy and implementation procedures protect waters that are better than the minimum specified for that designated use. For more information on Maryland's Tier II Antidegradation Policy please click HERE. To go directly to maps of Tier II high quality waters, please click HERE
  • The Tier III of protection (Tier 3), for waters designated as  Outstanding National Resource Waters or ONRW, provides the most stringent level of protection.  ​
  • Maryland's Antidegradation Regulations are provided in COMAR Sections (general), (Tier I), and (Tier II), and​ (Tier III). Click on each hyperlink to access that particular section.​

Current Water Quality Standards

For the full text of Maryland Water Quality Standards please visit COMAR Online to access 26.08.01 and 26.08.02.​

How are changes to water quality standards made?

Changes to the Water Quality Standards are implemented through regulatory changes which are subject to the normal promulgation process. Every three years, the Clean Water Act requires that States review their water quality standards in what is called the Triennial Review of Water Quality Standards (TR). The TR includes a robust public participation process prior to adoption of new or revised regulations. This process generally includes an Advanced Notice of Public Rule-Making (ANPRM) and solicitation of comments followed later by a more formal public comment period during which a hearing takes place (the formal comment period and hearing are required). Comments are incorporated and/or responded to in what becomes a public document as part of the TR package that EPA reviews. To see materials from Maryland's past Triennial Review actions please click here

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For more information, please contact Melinda Cutler at

Last Updated 5/2024

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