Antidegradation

Washington State Department of Ecology

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Antidegradation

The Clean Water Act requires that state water quality standards protect existing uses by establishing the maximum level of pollutants allowed in state waters. The standards must also protect those waters of a quality that are higher than the standards requirement. The antidegradation process helps prevent unnecessary lowering of water quality, and provides a framework to identify those waters that are designated as an “outstanding resource” by the state. Washington State’s antidegradation policy follows the the federal regulation guides, and has three tiers of protection.

Tier I. WAC 173-201A-310
Tier I is used to ensure existing and designated uses are maintained and protected. It does this by focusing on fully applying the water quality criteria and correcting problems using our existing regulatory and TMDL processes. Tier I applies to all waters and all sources of pollution.
Tier II. WAC 173-201A-320
Tier II is used to ensure that waters of a higher quality than the criteria assigned in the standards are not degraded unless such lowering of water quality is necessary and in the overriding public interest. Tier II applies only to new or expanded sources of pollution from specific types of activities directly regulated by Ecology (e.g., NPDES, 401, 404, Forest Practices). Any new or expanding dischargers that would cause a measurable degradation of water quality:
1. Must go through a technology review to identify and apply any feasible alternatives to that degradation.
2. Must show that overriding public benefits would occur from allowing the lowering of water quality.
See Tier II guidance (PDF) for more information.
Tier III. WAC 173-201A-330
Tier III is used when a high-quality water is designated as an “outstanding resource water.” The water quality and uses of these waters must be maintained and protected against all sources of pollution.

A request for designation of Tier III may be made by the Department of Ecology (department). A Tier III designation may also be requested through public nominations that are submitted to the department in writing. Public nominations must include sufficient information to show how the water body meets the appropriate conditions of an outstanding resource water. If the information proposed demonstrates that the waterbody meets the eligibility requirements, the department will schedule a review of the nominated water for designation. The review will include a public process and consultation with recognized tribes in the geographic vicinity of the water. The rules allow two levels of Tier III protection. A qualifying water body may be designated as:
- Tier III(A), which prohibits any and all future degradation [WAC 173-201A-330(5)(A)].
- Tier III(B), which allows for de minimis (below measurable amounts) degradation from well-controlled activities [WAC 173-201A-330(5)(B)].
For more information about the Tier III designation see:
- Requirements for Tier lll Antidegradation Eligibility.
- Frequently Asked Questions about Protecting High Quality Waters in Washington (Ecology publication)

EPA approved Washington State's Antidegradation Policy in May 2007: See formal letter (PDF)

Last updated February 2008