Surface water quality: Antidegradation

The federal Clean Water Act requires that our water quality standards protect existing designated uses by establishing the maximum level of pollutants we can allow in surface water. We require extra protections for water that is already cleaner than the standards. We also provide a framework to identify which water is designated as an “outstanding resource” by the state.

Three tiers of protection

Our antidegradation rules follow the federal regulations, which set three tiers of protection for surface water.

Tier I – applies to all water and all sources of pollution

Tier I ensures 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 Total Maximum Daily Load (TMDL) water cleanup processes.

Tier II – protects high quality water bodies

Tier II protects surface water that is currently higher quality than the limits set in the standards from degradation by new or expanded actions. A Tier II analysis may still result in lowering of water quality if Ecology determines that the action is necessary and in the overriding public interest.

Tier II is applied only to new or expanded sources of pollution from specific types of activities we regulate such as national pollutant discharge elimination system (NPDES) permits.

Any new or expanding discharges that would cause a measurable degradation of water quality must:

  • Maintain Tier I protection.
  • Go through a technology review to identify and apply any feasible alternatives to degrading water quality.
  • Show that overriding public benefits would be gained from allowing some lowering of water quality.

See Tier II guidance for more information.

Tier III – protects outstanding resource waters

Tier III sets protections for high quality water bodies designated as outstanding resource waters.

Outstanding resource waters can be designated as Tier III (A) or Tier III (B) protection:

  • Tier III (A) is the highest level of protection and allows no further degradation after the water has been formally designated.
  • Tier III (B) is the second highest level of protection and conditionally allows minor degradation to occur due to highly controlled actions described under WAC 173-201A-330(5)(b).

What water bodies are eligible?

To be eligible for designation as an outstanding resource water, a water body must have one or more characteristics relating to exceptional or unique water quality, recreational, or ecological value. The specific eligibility requirements are listed under WAC 173-201A-330(1).

Who can nominate an outstanding resource water?

We can request a Tier III designation, or we can receive written public nominations. Public nominations must include sufficient information to show how the water body meets the appropriate conditions of an outstanding resource water.

How is an outstanding resource water designated?

If the nomination demonstrates that the water body meets the eligibility requirements, we will schedule a review of the nominated water for designation. The review will include a public process and consultation with tribes in the geographic vicinity of the water.

To determine whether or not to designate a water body as an outstanding resource water, we consider factors relating to the social and economic impact of a designation and input from the public and local governments.

Outstanding resource waters in Washington

Adopted outstanding resource waters are listed in WAC 173-201A-332. Below you can read information about each designation.