Water Quality

​On January 7, 2015, the Environmental Quality Commission adopted, and on Aug. 4, 2015, the U.S. Environmental Protection Agency 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.


The revised ammonia criteria, based on EPA's latest recommendations, protect sensitive freshwater mussels and snails, including other aquatic species. Current information indicates that freshwater mussels and snails are present in many waterbodies across Oregon. The adopted criteria are expressed as Total Ammonia Nitrogen (NH3 and NH4) and continue to be dependent on the pH and temperature of water. 

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: