Hide Alert

Welcome to our new website. Learn more about what's new.

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. The standards must also be more protective of higher quality waters than the standards require.

Antidegradation rules help prevent unnecessary lowering of water quality. They also provide a framework to identify which waters are designated as an “outstanding resource” by the state.

Washington state's antidegradation rules follow the federal regulations, which set three tiers of protection for surface waters.

Three tiers of protection

Tier I

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 I applies to all waters and all sources of pollution.

Tier II

Tier II is used to ensure that waters that meet a higher quality than the limits set in the standards are not degraded. Waters may still be degraded if 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:

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

Tier III

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.

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.

If the information proposed 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 recognized tribes in the geographic vicinity of the water.

Outstanding resource waters can be designated for either Tier III(A) or Tier III(B) protection.

  1. Tier III(A) is the highest level of protection and allows no further degradation after the waters have been formally designated.
  2. 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:
    1. Sources of pollution — considered individually and cumulatively — are not to cause measurable degradation of the water body.
    2. Sources of pollution must use: 
      1. Applicable advance waste treatment and control techniques.
      2. Prevent runoff pollution from nonpoint sources.
      3. Reasonably represent state-of-the art-technology.
      4. Minimize the degradation of water quality to non-measurable levels (where total elimination is not feasible).

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:

  1. 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.
    1. The water body must be largely free from human sources of degradation.
  2. 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.
  3. The water has both high water quality and regionally unique recreational value.
  4. The water is of exceptional statewide ecological significance.
  5. 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 water body and input from citizens and local governments.