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Wetland Bioassessment Factsheet 7

United States Environmental Protection Agency
Office of Water
Office of Wetlands, Oceans and Watersheds (4502-F)
July 1998

Wetland Bioassessment Fact Sheet 7

The main objective of the Clean Water Act (CWA) is to "restore and maintain the chemical, physical, and biological integrity of the Nation's water." To help meet these objectives, states must adopt water quality standards (WQS) for all "waters of the U.S." within their boundaries, including wetlands. Water quality standards, at a minimum, consist of three major components: 1) designated beneficial uses, 2) narrative and numeric water quality criteria for supporting each use, and 3) an antidegradation statement.

1. Designated Uses

Designated uses establish the environmental goals for water resources. States and tribes assign designated uses for each water body, or segment of a body of water, within their boundaries. Typical uses include public water supply, primary contact recreation (such as swimming), and aquatic life support (including the propagation of fish and wildlife). States and tribes develop their own classification system and can designate other beneficial uses including fish consumption, shellfish harvesting, agriculture, wildlife habitat, and groundwater recharge.

Since designated uses can vary, states and tribes may develop unique water quality requirements or criteria for their designated uses. States and tribes can also designate uses to protect sensitive or valuable aquatic life or habitat, such as wetlands. When designating uses for wetlands, states may establish an entirely different format to reflect the unique functions and values of wetlands. At a minimum, designated uses must be attainable uses that can be achieved using best management practices and other methods to prevent degradation. States and tribes can also designate uses which have not yet been achieved or attained. Protecting and maintaining such uses may require the imposition of more stringent control programs.

2. Water Quality Criteria

The Water Quality Standards Regulation requires states to adopt criteria sufficient to protect and maintain designated uses. Water quality criteria may include narrative statements or numeric limits. States and tribes can establish physical, chemical, and biological water quality criteria. Wetland biological monitoring and assessment programs can help states and tribes refine their narrative and numeric criteria to better reflect conditions found in wetlands.

Narrative water quality criteria define conditions that must be protected and maintained to support a designated use. States should write narrative criteria to protect designated uses and to support existing uses under State antidegradation policies. For example, a state or tribe may describe desired conditions in a water body as "waters must be free of substances that are toxic to humans, aquatic life, and wildlife." In addition, states and tribes can write narrative biological criteria to describe the characteristics of the aquatic plants and animals. For example, a state may specify that "ambient water quality shall be sufficient to support life stages of all native aquatic species."

Narrative criteria should be specific enough that states and tribes can translate them into numeric criteria, permit limits, and other control mechanisms including best management practices. Narrative criteria are particularly important for wetlands, since states and tribes cannot numerically describe many physical and biological impacts in wetlands by using current assessment methods.

Numeric water quality criteria are specific numeric limits for chemicals, physical parameters, or biological conditions that states and tribes use to protect and maintain designated uses. Numeric criteria establish minimum and maximum physical, chemical, and biological parameters for each designated use. Physical and chemical numeric criteria can include maximum concentrations of pollutants, acceptable ranges of physical parameters, minimum thresholds of biological condition, and minimum concentrations of desirable parameters, such as dissolved oxygen.

States and tribes can adopt numeric criteria to protect both human health and aquatic life support. For example, numeric human health criteria include maximum levels of pollutants in water that are not expected to pose significant risk to human health. The risk to human health is based on the toxicity of and level of exposure to a contaminant. States and tribes can apply numeric human health criteria (such as for drinking water) to all types of water bodies, including wetlands.

Numeric chemical or physical criteria for aquatic life, however, depend on the characteristics within a water body. Since characteristics of wetlands (such as hydrology, pH, and dissolved oxygen) can be substantially different from other water bodies, states and tribes may need to develop some physical and chemical criteria specifically for wetlands.

Numeric biological criteria can describe the expected attributes and establish values based on measures of taxa richness, presence or absence of indicator taxa, and distribution of classes of organisms. Many states have developed biological assessment methods for streams, lakes, and rivers, but few states and tribes have developed methods for wetlands. Several states, including Florida, Maine, Minnesota, Montana, North Dakota, and Ohio are currently developing biological assessment methods for monitoring the "health" of wetland plant and animal communities. Wetland biological assessment methods are essential to establish criteria that accurately reflect conditions found in wetlands.

3. Antidegradation Policy

All state standards must contain an antidegradation policy, which declares that the existing uses of a water body must be maintained and protected. Through an antidegradation policy, states must protect existing uses and prevent water bodies from deteriorating, even if water quality is better than the minimum level established by the state or tribal water quality standards. States and tribes can use antidegradation statements to protect waters from impacts that water quality criteria cannot fully address, such as physical and hydrologic changes.

States and tribes can protect exceptionally significant waters as outstanding national resource waters (ONRW). ONRWs can include waters, such as some wetlands, with special environmental, recreational, or ecological attributes. No degradation is allowed in waters designated as ONRW. States can designate waters that need special protection as ONRWs regardless of how they ecologically compare to other waters. For example, although the water of a swamp may not support as much aquatic life as a marsh, the swamp is still ecologically important. A state or tribe could still designate the swamp as an ONRW because of its ecological importance.

Applications of WQS

WQS provide the foundation for a broad range of management activities. WQS can serve as the basis to:

  • Assess the impacts of nonpoint source discharges on waterbodies under CWA §319,
  • Assess the impacts of point source discharges on waterbodies under CWA §402,
  • Determine if federally permitted or licensed activities maintain WQS under CWA §401 water quality certification, and
  • Track and report if waterbodies are supporting their designated uses under CWA §305(b).

Additional Information

The following EPA publications provide more information about WQS for wetlands and other surface waters:

(Some of these are available on