An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »

Fact Sheet: Ocean Acidification and Marine pH Water Quality Criteria

April 2009

EPA has published a Notice of Data Availability (NODA) to provide interested parties with information that was submitted to EPA regarding ocean acidification and to solicit additional pertinent data or scientific information that may be useful in addressing ocean acidification. In addition, EPA is notifying the public of its intent to review the current aquatic life criterion for marine pH to determine if a revision is warranted to protect the marine designated uses of states and territories pursuant to Clean Water Act §304(a)(1). The NODA also solicits ideas for effective strategies by state and territorial water program managers to address the impacts of ocean acidification. EPA also requests information pertaining to monitoring marine pH and implementing pH water quality criteria. 

Ocean acidification refers to the decrease in the pH of the oceans caused by the uptake of carbon dioxide (CO2) from the atmosphere. Oceans have been absorbing about one-third of the anthropogenic CO2 emitted into the atmosphere since pre-industrial times. As more CO2 dissolves in the ocean, it reduces ocean pH, which changes the chemistry of the water. These changes present potential risks across a broad spectrum of marine ecosystems.

The marine or saltwater pH criteria EPA recommended pursuant to Section 304(a) of the CWA applies to coastal waters specifically. States, territories and authorized tribes adopt saltwater pH criteria into their water quality standards, as appropriate, to protect the designated use of the coastal waters within their jurisdiction. EPA received a petition from the Center for Biological Diversity (CBD) requesting that EPA revise its recommended national marine pH water quality criterion for the protection of aquatic life and asking EPA to publish information and provide guidance on ocean acidification.

EPA has agreed to publish a NODA in the Federal Register to present available information on this issue and to solicit scientific views on the following specific issues:

  • Technical information on measurement of ocean acidification in marine coastal waters.
  • Technical information on effects of ocean acidification on marine biota.
  • Scientific views on the information presented in the bibliography provided in the notice.
  • Information related to the existing recommended pH criterion for marine waters, including how the criterion could be best expressed, particularly with respect to natural variability.
  • Information regarding state and territorial implementation of the pH criterion related to new information on ocean acidification.
  • Potential strategies for state and federal water programs to coordinate and enhance federal data collection efforts.
  • Information that may be used to develop guidance and information on ocean acidification pursuant to Clean Water Act Section 304(a)(2) for states and the public.

After the comment period for the NODA closes, EPA plans to evaluate the information and data it has received on ocean acidification. EPA intends to make a final decision, within one year of the date of publication of the NODA, on whether revisions to the current pH water quality criterion are needed.

To get more information, contact Joe Beaman ( at 202-566-0420 or Lisa Huff ( at 202-566-0787.

Top of Page