River valley photo.  Photographer unknown.

Surface Water Criteria

Water quality criteria, for fresh or marine waters, are developed to provide protection for designated uses. Criteria may be numeric (i.e., not to exceed some concentration) or narrative. Water quality criteria are applied alongside the designated use associated with every waterbody in the state. The Water Quality Standards contain numeric and narrative criteria for both marine and fresh waters.

Numeric Criteria

Numeric criteria are developed to protect designated uses. Individual numeric criteria are based on specific data and scientific assessment of adverse effects. The numeric criteria are numbers that specify limits and/or ranges of chemical concentrations, like oxygen, or physical conditions, like water temperature. A typical numeric criterion for aquatic life protection usually contains a concentration (e.g. 5 mg/L) and averaging period. For example, for toxics a one-hour averaging period applies for an acute (short-term) concentration, while a four-day average applies for a chronic (long-term) concentration. The criteria are values that should rarely be exceeded if uses are to be supported.

Parameter or Type Freshwater Criteria Marine Criteria

Waters Requiring Supplemental Spawning and Incubation Protection for Salmonid Species (Ecology publication)

For more information on temperature criteria click here.

WAC-173-201A-200 (1)(c)
Table 200 (1)(c)
Table 210 (1)(c)
Dissolved Oxygen WAC-173-201A-200 (1)(d)
Table 200 (1)(c)
Table 210 (1)(d)
Total Dissolved Gas WAC-173-201A-200 (1)(f)
Table 200 (1)(c)

No Marine Criteria for Total Dissolved Gas

pH WAC-173-201A-200 (1)(g)
Table 200 (1)(c)
Table 210 (1)(f)
Turbidity WAC-173-201A-200 (1)(e)
Table 200 (1)(c)
Table 210 (1)(e)
Bacteria WAC-173-201A-200 (2)(b)
Table 200 (1)(c)
Table 210 (3)(b)

For more information on nutrients criteria click here.

WAC 173-201A-230 (Code Reviser)
Table 230 (1)

For more information on toxics criteria click here.

WAC-173-201A-240 (Code Reviser) WAC-173-201A-240 (Code Reviser)
Table 240(3)
Radioactive Substances

WAC-173-201A-250 (Code Reviser)

Natural Conditions and Narrative Criteria WAC-173-201A-260 (Code Reviser)


Narrative Criteria

Washington adopted narrative criteria to supplement numeric criteria. The narrative criteria are statements that describe the desired water quality goal, such as waters being "free from" pollutants such as oil and scum, color and odor, and other substances that can harm people and fish. These criteria are used for pollutants for which numeric criteria are difficult to specify, such as those that offend the senses (e.g., color and odor).

Understanding Units of Measure

Numeric criteria and technical reports express the amounts of different contaminants in water samples in metric units. These units of measurement can be confusing. Here are unit conversion tables to use.

Further explanations and conversion are presented on Water on the Web, a collaborative effort by education, tribal organizations, industry and natural resource and regulatory agencies.


View the Water Quality Standards

Please be sure to refer to the full version of the standards for additional information on each specific water quality criteria that may need to be applied:

Code Reviser version
Easy to read version

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Last updated November 2011