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Maryland State Government Maryland Department of the Environment

Water Quality Standards



The Clean Water Act (CWA) requires that States review their water quality standards (WQS) every three years (Triennial Review) and revise the standards as necessary.  A water quality standard consists of three parts:

  • Designated Uses that set goals for a water body.  Examples are support of aquatic life, drinking water supply or a coldwater fishery such as trout.
  • Criteria that support the designated uses - There are numerous criteria for chemical substances, bacteria, acidity and physical characteristics (e.g., temperature).  Examples include dissolved oxygen sufficient to support aquatic life or metals in sufficiently low concentrations that they will not interfere with aquatic life.
  • Antidegradation policy - Maryland has a policy in place, and updates the list of high quality waters each triennium as needed. 

Maryland's water quality standards are found in the Code of Maryland regulations (COMAR) at 26.08.01 – 26.08.02. Maryland regulations may be accessed online at the Division of State Documents web site:  Click on COMAR Online and enter the appropriate regulatory reference.

On April 2, 2014, the Secretary of the Environment adopted amendments to the water quality standards regulations.  These amendments were proposed in the December 13, 2013 edition of the Maryland Register (40:20 Md. R.) Final action on the regulations is published in the April 18 edition of the Maryland Register.  Click here: Maryland Register Online

Opportunity for public comment:

Comments specific to this proposal were received and have been addressed in this comment/response document.  Click HERE


 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 are three components of water quality standards:

  • Designated Uses;
  • Water quality criteria to protect the designated uses; 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.


 Water Quality Criteria

  • Numeric criteria set the minimum water quality to meet the designated uses.
  • Maryland has numerous numeric criteria for protection of aquatic life and human health (e.g., 5 mg/l for dissolved oxygen; 82 mcg/l for Pb (acute, freshwater))
  • Criteria are published for toxics, dissolved oxygen, turbidity, bacteria, and temperature.
  • Where specific numeric criteria are not available (e.g., oil, grease, odor, nuisance), narrative criteria apply.

Numerical Criteria for Toxic Substances in Surface Waters: COMAR - Go to COMAR Online at


Water Quality Criteria Specific to Designated Uses: COMAR - Go to COMAR Online at



  • Maryland’s antidegradation policy assures that water quality continues to support designated uses.
  • EPA regulations provide for three tiers of protection:
    • Tier 1 specifies the minimum standard that must be met—support of balanced indigenous populations and support of contact recreation—this is often referred to as "fishable-swimmable."
    • Tier 2 protects water that is 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 2 high quality waters, please click HERE
    • Maryland is developing the third Tier of protection (Tier 3) called an Outstanding National Resource Water or ONRW.  

COMAR - Go to COMAR Online at


Current Water Quality Standards

For the text of Maryland Water Quality Standards please check COMAR 26.08.02

Changes to the Water Quality Standards

Changes to the Water Quality Standards are implemented through regulatory changes which are subject to the normal promulgation process.

  • Every three years, the CWA requires that States review their water quality standards.
  • Active public involvement is a clear priority.


Factsheets:  Frequently Asked Questions about Chesapeake Bay Water Quality Standards

                     Frequently Asked Questions about EPA's 2012 Recreational Water Quality Criteria


For more information, please contact John Backus at  or at (410) 537-3965.

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