Aquatic Life Ambient Water Quality Criteria for 

Ammonia - Freshwater (2013) 

Summary

EPA has published national recommended 

ambient water quality criteria for the protection 

of aquatic life from the toxic effects of 

ammonia, a constituent of nitrogen pollution. 

These recommended criteria will help States, 

Territories, and authorized Tribes update their 

water quality standards with concentration levels

for ammonia in surface waters at or below which 

aquatic organisms will be protected, if not 

exceeded more frequently than once every three 

years on average. Acute and chronic criteria 

were developed to protect organisms from both 

immediate effects, such as mortality, and longerterm effects on reproduction, growth and 

survival, respectively. 

EPA’s final Aquatic Life Ambient Water Quality 

Criteria for Ammonia – Freshwater (2013) 

incorporate scientific views received on EPA's

2009 draft updated ammonia criteria and 

supersede EPA’s previously recommended 1999 

ammonia criteria. 

What are national recommended aquatic life

ambient water quality criteria?

Ambient water quality criteria for the protection 

of aquatic life are numeric concentrations of 

pollutants, with specific associated duration and 

frequency information, in surface waters that are 

protective of aquatic life designated uses. Under 

Clean Water Act section 304(a), EPA is required 

to develop and publish water quality criteria that

reflect the latest scientific knowledge. Water 

quality criteria are based solely on data and 

scientific judgments about the relationship 

between pollutant concentrations and potential 

environmental and human health effects. EPA's 

recommended water quality criteria are not 

rules, nor do they automatically become part of a 

state's water quality standards. States must adopt 

into their standards water quality criteria that 

protect the designated uses of the water bodies 

within their area. These can include 

scientifically defensible site-specific criteria that 

are different from EPA's national recommended

criteria, as long as the site-specific criteria are 

protective of the designated use. Water quality 

criteria are not effective under the Clean Water 

Act until they have been adopted into a state’s 

water quality standards and approved by EPA.

What is ammonia?

Ammonia is one of several forms of nitrogen 

that exist in aquatic environments. Unlike other 

forms of nitrogen, which can cause nutrient 

over-enrichment of a water body at elevated 

concentrations and indirect effects on aquatic 

life, ammonia causes direct toxic effects on 

aquatic life. 

Ammonia is produced for commercial fertilizers 

and other industrial applications. Natural sources 

of ammonia include the decomposition or 

breakdown of organic waste matter, gas 

exchange with the atmosphere, forest fires, 

animal and human waste, and nitrogen fixation 

processes.

How does ammonia enter surface waters?

Ammonia can enter the aquatic environment via 

direct means such as municipal effluent 

discharges and the excretion of nitrogenous 

wastes from animals, and indirect means such as 

nitrogen fixation, air deposition, and runoff from 

agricultural lands. 

How does ammonia affect aquatic life?

When ammonia is present in water at high 

enough levels, it is difficult for aquatic 

organisms to sufficiently excrete the toxicant, 

leading to toxic buildup in internal tissues and 

blood, and potentially death. Environmental 

factors, such as pH and temperature, can affect 

ammonia toxicity to aquatic animals. 

Office of Water 820-F-13-013

MC 4304T August 2013 
What is the history of EPA’s development of

ammonia criteria?

EPA first published ammonia criteria for the 

protection of aquatic life in 1976. The criteria 

were then updated in 1985 and 1999 to reflect 

scientific information available at that time. The 

1999 recommended aquatic life criteria for 

ammonia were based on the most sensitive 

endpoints known at the time: the acute criterion 

was based on salmonid fish toxicity information, 

and the chronic criterion was based on bluegill 

sunfish early life stage toxicity. 

In 2003, EPA became aware of new toxicity 

studies indicating the relative sensitivity of 

freshwater mussels to ammonia and began to 

update the 1999 criteria to reflect this new 

information. In 2009, following external peer 

review, EPA published draft recommended

ammonia criteria, for waters with and without 

mussels. Since the publication of the draft 2009 

ammonia criteria, additional toxicity testing has 

validated information on the effects of ammonia 

on sensitive freshwater gill-breathing snail

species. In April 2013, EPA finalized the 

updated ammonia criteria that are applicable 

nationally, taking into account the latest toxicity 

information for freshwater species, including

unionid mussels and gill-breathing snails. The 

2013 criteria incorporate scientific views 

received on the draft (2009) ammonia criteria 

and supersede EPA’s previously recommended 

1999 criteria.

What are the 2013 recommended water

quality criteria for ammonia?

EPA recommends an acute criterion magnitude 

of 17 mg Total Ammonia Nitrogen (TAN) per 

liter at pH 7 and 20°C for a one-hour average

duration, not to be exceeded more than once 

every three years on average. EPA recommends

a chronic criterion magnitude of 1.9 mg TAN/L

at pH 7 and 20°C for a 30-day average duration,

not to be exceeded more than once every three 

years on average. In addition, the highest fourday average within a 30-day period should not 

exceed 2.5 times the chronic criterion magnitude 

(e.g. 1.9 mg TAN/L x 2.5 = 4.8 mg TAN/L at 

pH 7 and 20°C) more than once in three years on 

average. 

How do the 2013 criteria compare to the

previously recommended 1999 criteria and

the draft 2009 criteria?

The 2013 ammonia criteria recommendations 

take into account the latest freshwater toxicity 

information for ammonia, including toxicity 

studies for sensitive unionid mussels and gillbreathing snails. These new criteria are based on 

robust toxicity data available for 69 genera 

(acute) and 16 genera (chronic). The updated 

criteria magnitudes are more stringent than the 

previously recommended 1999 criteria

magnitudes (see Table 1). The duration

components of the 1999, 2009 and 2013 criteria 

remain the same - a one-hour average duration

for the acute criterion and 30-day average

duration for the chronic criterion. The frequency 

component for the acute and chronic criteria

remains once in three years on average.

Table 1. Comparison of past and current EPArecommended aquatic life water quality criteria 

magnitudes for ammonia. Criteria magnitudes 

are expressed as total ammonia nitrogen (mg

TAN/L) at pH 7 and 20°C.

Criterion

Duration

1999 

Criteria 

2009 

Draft 

Updated

Criteria 

2013 

Final 

Updated

Criteria 

Acute

(1-hour 

average)

24 19 17

Chronic

(30-day

rolling 

average)

4.5* 0.91* 1.9*

*Not to exceed 2.5 times the criterion 

continuous concentration as a 4-day average 

within a 30-day period. 

Criteria frequency: Not to be exceeded more 

than once in three years on average.
Additional EPA Resources

EPA has developed three supporting documents 

to aid states considering adoption of the 2013

recommended ammonia criteria.

Flexibilities for States Applying EPA’s Ammonia 

Criteria Recommendations provides an 

overview of a number of implementation 

approaches available for state consideration, 

including the recalculation procedure for sitespecific criteria derivation, variances, revisions

to designated uses, dilution allowances, and 

compliance schedules. The document describes 

how each of these flexibilities fits within a 

state’s water quality standards adoption and 

implementation processes.

EPA has also developed a Revised Deletion 

Process for the Site-Specific Recalculation 

Procedure for Aquatic Life Criteria that 

describes a recalculation procedure and includes 

a spreadsheet that may be used to derive sitespecific water quality criteria for the protection 

of aquatic life in order to best reflect the 

organisms that reside at a specific site. 

A third document, which EPA expects to publish 

in 2013, Technical Support Document for 

Conducting and Reviewing Freshwater Mussel 

Studies for the Development of Site-specific 

Water Quality Criteria for Ammonia, will help 

states determine if sensitive freshwater mussels 

are present in their waters. Commonly-used 

mussel sampling methods will be described and 

an overview will be provided of various study 

approaches, considerations, and limitations, 

including real-life examples. 

How to View the Criteria Document and

Supporting Information

EPA has established an official public docket for 

this action under Docket ID No. EPA-HQ-OW2009-0921, accessed at www.regulations.gov. 

You may also download the document and 

supporting information from 

http://water.epa.gov/scitech/swguidance/standar

ds/criteria/aqlife/ammonia/index.cfm.

For More Information

Contact Lisa Huff by telephone at (202) 566-

0787, by email at huff.lisa@epa.gov, or by mail 

at U.S. EPA, MC: 4304T, 1200 Pennsylvania 

Ave., N.W., Washington, D.C. 20460.