Maryland's Designated Uses, Water Quality Standards

Maryland's Designated Uses for Surface Waters

To go directly to maps of Maryland's use classes/designated uses please click HERE. For general information on Maryland's use classification system, please read below.

Each water body in Maryland is assigned a use class. The use class is a grouping or set of designated uses that apply to a water body which individually may or may not be supported now, but should be attainable.

The State of Maryland has defined the Use Classes below.  Provided next to these are general descriptions of the specific designated uses included within these Use Classes.

  • Use Class I: Water Contact Recreation, and Protection of Nontidal Warmwater Aquatic Life
  • Use Class I-P: Water Contact Recreation, Protection of Aquatic Life, and Public Water Supply

  • Use Class IISupport of Estuarine and Marine Aquatic Life and Shellfish Harvesting+
    • Shellfish Harvesting Subcategory
    • Seasonal Migratory Fish Spawning and Nursery Subcategory (Chesapeake Bay only)
    • Seasonal Shallow-Water Submerged Aquatic Vegetation Subcategory (Chesapeake Bay only)
    • Open-Water Fish and Shellfish Subcategory (Chesapeake Bay only)
    • Seasonal Deep-Water Fish and Shellfish Subcategory (Chesapeake Bay only)
    • Seasonal Deep-Channel Refuge Use (Chesapeake Bay only)

+Waterbodies designated as Use II do not necessarily support the shellfish harvesting use as some waters may be tidal but too fresh to support viable populations of shellfish.

  • Use Class II-P: Tidal Fresh Water Estuary – includes applicable Use II and Public Water Supply
  • Use Class III: Nontidal Cold Water
  • Use Class III-P: Nontidal Cold Water and Public Water Supply
  • Use Class IV: Recreational Trout Waters
  • Use Class IV-P: Recreational Trout Waters and Public Water Supply

 The following table shows the individual designated uses included in each use class grouping.


 *All of the "seasonal" (plus the Open Water Fish and Shellfish) designated use subcategories only apply to the Chesapeake Bay and its tidal tributaries.

For more detailed information describing Maryland’s designated uses please visit the Code of Maryland Regulations (COMAR) Sections and

For official information on where these designated uses apply please see COMAR Section  These geographical descriptions can be difficult to decipher.  To make this easier, MDE has created a dynamic map that displays the use classes that apply to each surface water body.  Click on the Designated Uses Mapping Page to view these maps.

Existing Uses (EU)

A lesser-known portion of both Federal and State water quality standards deals with the concept of existing uses.  “Existing uses are those uses actually attained in a waterbody on or after November 28, 1975, whether or not they are included in the water quality standards.”(Code of Federal Regulations (CFR) Title 40 § 131.3)  Additionally, the Federal regulations discuss existing uses in 40 CFR § 131.12(a), stating that “at a minimum…(1) Existing instream water uses and the level of water quality necessary to protect the existing uses shall be maintained and protected.”  In other words, existing uses could be described as a baseline or ‘floor’ of water quality that should be maintained and protected.  Also, existing uses can be expressed more specifically than designated uses, to reflect the degree of use actually attained.  The main difference between existing uses and designated uses is that designated uses describe the attainable condition while existing uses describe the past or present condition of a water body.

Updating Uses for Particular Water Bodies

In certain water bodies, the currently designated use class may not accurately reflect the existing use of a water body. In these cases, MDE may pursue use redesignation to better characterize and protect the existing use. One such example may occur when a currently designated Use Class I (warmwater) stream has documented coldwater obligate species (e.g. brook trout, Tallaperla sp.). In this scenario, the Department will apply the recently developed "Use Class Re-Designation Procedures for Streams that have a Cold Water existing use" to determine if the use class should be updated to Use Class III (coldwater). If the water body meets the conditions specified in this decision document, MDE will propose the use redesignation during the next Triennial Review.   

Contact Info

Please direct questions or comments concerning Maryland's Water Quality Standards to Matthew Stover at or 410-537-3611.​