Chapter 173-201A WAC (Natural Conditions)

The Washington State Department of Ecology is considering revising Chapter 173-201A WAC, Water Quality Standards for Surface Waters of the State of Washington.

We are considering revisions to several natural conditions provisions in our surface water quality standards. We have natural conditions provisions in our rule because conditions in some surface waters naturally do not meet water quality criteria. For example, a naturally low-flowing stream in a natural prairie without any human alteration may have seasonally higher temperatures than the limit set to protect fish. These inconsistencies may be due to natural processes or seasonal conditions that prevent a water body from meeting the applicable aquatic life criteria.

Our goal is to refine the natural conditions criteria to protect characteristics unique to a specific water. 

We will evaluate the latest scientific data, methods, modeling tools, and approaches to update natural conditions provisions necessary for refining aquatic life protection in our surface waters. As part of this process, we will consider the Environmental Protection Agency’s recommended approaches for natural conditions in water quality standards. 

Specifically, we are considering amendments to:

  • WAC 173-201A-200(1)(c), Aquatic life temperature criteria, including, but not limited to, subsection (i).
  • WAC 173-201A-200(1)(d), Aquatic life dissolved oxygen (D.O.) criteria including, but not limited to, subsection (i)
  • WAC 173-201A-210(1)(c), Aquatic life temperature criteria including, but not limited to, subsection (i).
  • WAC 173-201A-210(1)(d), Aquatic life dissolved oxygen (D.O.) including, but not limited to, criteria subsection (i).
  • WAC 173-201A-260(1), Natural and irreversible human conditions.
  • WAC 173-201A-310(3), Tier I – Protection and maintenance of existing and designed uses.

We may amend other sections of Chapter 173-201A WAC as necessary to be consistent with or provide support to any revisions to the sections noted above.

Rulemaking timeline


Announcement phase (CR-101)

Filing date:
Sept. 27, 2022

Announcement documents

Rule development phase

Additional languages

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To request ADA accommodation for disabilities, or printed materials in a format for the visually impaired, contact Ecology's ADA Coordinator by email at, or call 360-407-6831. People with impaired hearing may call Washington Relay Service at 711. People with speech disability may call TTY at 877-833-6341.