Element 6 - Overview

Missouri’s Water Quality Standards provide the basis for the department’s Water Protection Program. Water quality standards consist of three components: designated beneficial uses, water quality criteria, and an antidegradation policy. As required by the Clean Water Act, the department reviews and modifies the water quality standards ever three years. Termed the triennial review process, the department evaluates the effectiveness of the standards and proposes new or revised standards accordingly.

Additional information regarding Missouri’s water quality standards are online at the department's website. Proposed changes to Missouri’s water quality standards can be found on the department’s Rules in Development web page

Designated Uses:

Designated beneficial uses are the uses for a water body identified in the state water quality standards that must be maintained in accordance with the federal Clean Water Act.

As a goal, the department, through a stakeholder process, will designate Clean Water Act Section 101(a) presumed uses to additional waters of the U.S. The department will review comments received from the public indicating existing uses and propose appropriate designated use changes as part of the triennial review process.

As a goal, the department will evaluate its current aquatic life use designations and consider the appropriateness of these uses and options for moving towards a tiered aquatic life structure.

The department will review use attainability analyses submitted to it and determine the appropriateness of any use changes.

As a goal, the department, through a stakeholder process, will develop an aquatic life use attainability analysis protocol.

Water Quality Criteria:

Water quality criteria are limits on particular chemicals or conditions in a water body to protect particular designated beneficial uses. Water quality criteria can be expressed as specific numeric criteria or as general narrative statements.

The department will, as part of its triennial review, evaluate the appropriateness of its water quality criteria for protecting its designated uses.

As a goal, the department will develop nutrient criteria for the protection of aquatic life in classified streams and lakes. More information regarding the state’s development of nutrient criteria can be found at

The department will review data submitted to it and evaluate the appropriateness for site-specific criteria.

As part of the triennial review, the department will review EPA 304(a) recommended criteria and adopt these criteria or propose its own criteria when appropriate.

As a goal, should the department adopt a tiered aquatic life scheme, the department will develop appropriate aquatic life protections consistent with these uses.


Missouri’s Water Quality Standards include the EPA “three-tiered” approach to antidegradation, and may be found at 10 CSR 20-7.031(2).

Tier 1 – Protects existing uses and a level of water quality necessary to maintain and protect those uses. Tier I provides the absolute floor of water quality for all waters of the United States. Existing instream water uses are those uses that were attained on or after Nov. 28, 1975, the date of EPA’s first Water Quality Standards Regulation.

Tier 2 – Protects and maintains the existing level of water quality where it is better than applicable water quality criteria. Before water quality in Tier 2 waters can be lowered, there must be an antidegradation review consisting of: (1) a finding that it is necessary to accommodate important economic and social development in the area where the waters are located; (2) full satisfaction of all intergovernmental coordination and public participation provisions; and (3) assurance that the highest statutory and regulatory requirements for point sources and best management practices for nonpoint sources are achieved. Furthermore, water quality may not be lowered to less than the level necessary to fully protect the “fishable/swimmable” uses and other existing uses.

Tier 3 – Protects the quality of outstanding national and state resource waters, such as waters of national and state parks, wildlife refuges and waters of exceptional recreational or ecological significance. There may be no new or increased discharges to these waters and no new or increased discharges to tributaries of these waters that would result in lower water quality.

More information regarding to Missouri’s anti-degradation policy can be found on the department’s antidegradation web pages.