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

Washington state's 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

Tier II is used to ensure that water that is currently higher quality than the limits set in the standards are not degraded. Tier II water may still be degraded if Ecology determines that impacting 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 we directly regulate  — such as national pollutant discharge elimination system (NPDES) permits.

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

  • Go through a technology review to identify and apply any feasible alternatives to degrading water quality.
  • Show that overriding public benefits would occur from allowing the lowering of water quality.

See Tier II guidance for more information.

Tier III

Tier III is used when a high-quality waterbody is designated as an outstanding resource water. The water quality and uses of this water must be maintained and protected against all sources of pollution.

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

If the nomination demonstrates that the waterbody 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 recognized tribes in the geographic vicinity of the water.

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. The requirements for Tier III (B) are:

  • Sources of pollution — considered individually and cumulatively — are not to cause measurable degradation of the waterbody.
  • Sources of pollution must use: 
    • Applicable advance waste treatment and control techniques.
    • Prevent runoff pollution from nonpoint sources.
    • Reasonably represent state-of-the art-technology.
    • Minimize the degradation of water quality to non-measurable levels (where total elimination is not feasible).

Read Frequently Asked Questions about Protecting High Quality Waters in Washington.

Tier III antidegradation eligibility

To be eligible for designation as outstanding resource water in Washington, the water must have one or more of the following characteristics:

  • The water is in a relatively pristine condition or possesses exceptional water quality, and also occurs in federal and state parks, monuments, preserves, wildlife refuges, wilderness areas, marine sanctuaries, estuarine research reserves, or wild and scenic rivers.
  • The water body must be largely free from human sources of degradation.
  • The water has unique aquatic habitat types — such as peat bogs — that by conventional water quality parameters — like dissolved oxygen, temperature, or sediment — are not considered high quality, but are unique and regionally rare examples of their kind.
  • The water has both high water quality and regionally unique recreational value.
  • The water is of exceptional statewide ecological significance.
  • The water has cold water thermal refuges critical to the long-term protection of aquatic species. For this type of outstanding resource water, the non-degradation protection would apply only to temperature and dissolved oxygen.

To determine whether or not to designate a water body as an outstanding resource water, we consider factors relating to the difficulty of maintaining the current quality of the waterbody and input from the public and local governments.

Nominations for outstanding resource waters