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 II guidance for more information.
For more information about the Tier III designation see:
EPA approved Washington State's Antidegradation Policy in May 2007: See formal letter (PDF)
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