U.S. flag An official website of the United States government.
				Here's how you know we're official. **Official websites use .gov** A **.gov** website belongs to an official government organization in the United States.
 **Secure websites use HTTPS** A small lock or **https://** means you’ve safely connected to a .gov website. Share sensitive information only on official, secure websites.


Toggle navigation Toggle search National Ocean Service National Oceanic and Atmospheric Administration
 Search
					Search National Ocean Service


Home
				Ocean Facts

				Topics
					Explore All Topics 
                        Arctic 
                        Careers 
                        Economy 
                        Ecosystems 
                        Geodesy 
                        Hazards 
                        International
                        Navigation 
                        Observations 
                        Ocean 
                        Recreation 
                         Sea Level Rise 
                        Story Maps 
                        Tools
                
                			Education

				
				News
				Podcasts
				Video
				Images
				About Us


1. Home
2. Facts
3. What is a dead zone?

**What is a dead zone?**  "Dead zone" is a more common term for **hypoxia**, which refers to a **reduced level of oxygen** in the water. A graphic that shows 2023 hypoxic zone in the Gulf of Mexico***At 3,058 square miles, the 2023 hypoxic zone in the Gulf of Mexico is the 7th smallest ever measured in the 37-year record, measured from July 23 to July 28, 2023. Red area denotes 2 milligrams per liter of oxygen or lower, the level which is considered hypoxic, at the bottom of the seafloor. (Bottom panel) Long-term measured size of the hypoxic zone (green bars) measured during the ship surveys since 1985, including the target goal established by the Mississippi River/Gulf of Mexico Watershed Nutrient Task Force and the 5-year average measured size (black dashed lines). Graphic credit: Louisiana Universities Marine Consortium***  Less oxygen dissolved in the water is often referred to as a “dead zone” because most marine life either dies, or, if they are mobile such  as fish, leave the area. Habitats that would normally be teeming with life  become, essentially, biological deserts. Hypoxic zones can occur naturally, but scientists are  concerned about the areas created or enhanced by human activity. There are many  physical, chemical, and biological factors that combine to create dead zones,  but nutrient pollution is the primary cause of those zones created by humans. Excess  nutrients that run off land or are piped as wastewater into rivers and coasts  can stimulate an overgrowth of algae, which then sinks and decomposes in the  water. The decomposition process consumes oxygen and depletes the supply  available to healthy marine life. Dead zones occur in coastal areas around the nation and in the Great Lakes — no part of the country or the world is immune. The second largest dead zone in the world is located in the U.S., in the northern Gulf of Mexico.
 More **Information** Hypoxia Primer National Centers for Coastal Ocean Science Dealing with Dead Zones: Interview with NOAA Hypoxia Expert (audio podcast) Hypoxia and Nutrient Pollution Overview Hypoxia in the Northern Gulf of Mexico What is eutrophication?   Get **Social** Social
  **Last updated:** 08/02/23 **Author:** NOAA How to cite this article Contact Us


Feedback Provide Feedback
							Contact Us
							Report an error
 Social Instagram Logo/a>


*Science. Service.Stewardship.*
 About NOS About Us
							NOS Program Offices
							Media Inquiries
							Website Acknowledgements
                            Site Index
							Disclaimer
 More Resources Freedom of Information Act
							Accessibility
							Information Quality
							Privacy Policy
							NOS For Employees
							USA.gov
 Department of Commerce
									National Oceanic and Atmospheric Administration (NOAA)
									National Ocean Service