Water Quality

Water quality standards are the foundation of the water quality-based control program mandated by the federal Clean Water Act. Water quality standards define goals for surface waters in Oregon by designating uses, setting criteria to protect those uses and establishing provisions to protect water quality from pollutants.

DEQ is responsible for establishing water quality criteria for toxic pollutants to protect both aquatic life and human health. These criteria are established to protect surface water for aquatic life use, allow Oregonians to consume fish and shellfish, and to use state waters for drinking water supply without adverse health effects. DEQ develops its water quality criteria based on EPA recommended criteria. 

Current toxics standards

Toxics standards rule - OAR 340-041-0033

Tables 30, 31 and 40 

  • Aquatic life criteria - Table 30
  • Human health criteria -Table 40
  • Guidance values ONLY - Table 31

Human health toxics criteria

On Oct. 17, 2011, EPA approved revisions to Oregon’s criteria to protect human health. The revised criteria shown in Table 40 above reflect a per-capita fish consumption rate of 175 grams/day (where applicable). See Human Health Water Quality Standards Rulemaking for more information about these revisions.


Aquatic life toxics criteria

On Jan. 31, 2013, EPA disapproved a number of aquatic life criteria that the Environmental Quality Commission adopted in 2004. The pollutants included pesticides, cadmium (acute only), copper, ammonia and aluminum. Since 2013, DEQ adopted and EPA approved revisions to several of the disapproved criteria.  

On Jan. 9, 2017, EPA approved the revisions to Oregon‘s freshwater aquatic life standard for copper. For more information, see the Copper Rulemaking website.
On Jan. 10, 2017, EPA signed a final rule to promulgate an acute freshwater aquatic life criteria for cadmium for Oregon into federal regulations. See additional information for acute cadmium under implementation for toxics criteria below.

On Aug. 4, 2015, EPA approved revisions to Oregon’s ammonia water quality standards for the protection of aquatic life. These criteria are now effective for all Clean Water Act programs in Oregon. Table 30 above contains the effective ammonia criteria. DEQ will update Oregon Administrative Rules 340-041-0033 and 340-041-8033 to reflect EPA’s approval in a subsequent rulemaking.    

See Ammonia Rulemaking for more information about these revisions. 
On April 11, 2014, EPA approved revisions to several pesticide criteria, the selenium criteria and other minor corrections and clarifications. See EPA's approval letter for more information.

Implementation information for Toxics Criteria

Calculator for freshwater hardness-dependent metals criteria

The toxicity of a metal to an aquatic organism can vary based on many different factors, including route of exposure to the metal, type and form of the metal and the physical/chemical characteristics of the water where the exposure takes place. Oregon’s aquatic life criteria for certain metals are based on water hardness. Generally, as hardness increases, the toxicity of metals decreases. The calculator below provides acute and chronic criteria for certain metals based on water hardness.


Acute cadmium criterion

The new federal acute hardness-based criterion for cadmium changes the hardness-based equation coefficients for the acute cadmium criterion and establishes new default hardness values by region. However, the new federal rule is not yet effective. It will become effective 30 days after it is published in the federal register. See metals calculator above.

Calculators for ammonia criteria

The chemical form of ammonia in water consists of two species—ammonium (NH4+) and unionized ammonia (NH3). The more toxic form of ammonia to aquatic life is un-ionized ammonia. The ratio of these species in freshwater is dependent on both pH and temperature. As pH and temperature increase the proportion of the un-ionized, more toxic form, of ammonia also generally increases. Consequently, the ammonia criteria become more stringent under these conditions.

The following saltwater calculator provides values for acute and chronic saltwater criteria based on pH, temperature, salinity and pressure. The saltwater ammonia criteria are based on EPA recommendations made in 1989 in Section 304(a) of the Clean Water Act. The final values in the calculator reflect the conversion of un-ionized ammonia to total ammonia nitrogen. 

The freshwater ammonia criteria provides values for acute and chronic freshwater criteria based on pH and temperature. The criteria are the values provided in the lookup tables in OAR 340-041 Table 30(a), 30(b), and 30(c).

The following calculator is provided for convenience, and provides the same criteria as the values contained in the look-up tables.

Note: On November 19, 2018, EPA gave notice of a typesetting error in the 2013 National Aquatic Life Ambient Water Quality Criteria for Ammonia. A parenthesis was omitted from the equation for freshwater acute criteria when salmonid species are absent. This equation appears in OAR-340-041 Table 30(b). This correction does not affect the criteria values in Table 30(b). The correct form of the equation is:


Copper Biotic Ligand Model

The Biotic Ligand Model software and information on implementation procedures are available on the Copper Standards web page.


Recommendations for analysis and implementation of specific toxic pollutants

Below is a list of memos that describe analytical methods for specific pollutants, including associated implementation and monitoring considerations. DEQ developed these memos to provide guidance to DEQ staff and other interested members of the public in response to analytical questions that have been raised on specific water quality toxics criteria. Additional memos may be posted here as other questions arise. 


Related links

Oregon Health Authority
Washington Department of Ecology
U.S. Environmental Protection Agency