Occurs when dissolved oxygen concentration in water drops very low, typically below 2 milligrams per liter; a level where most organisms become very stressed or cannot survive
US Department of Commerce, National Oceanic and Atmospheric Administration, Glossary - NOAA's State of the Coast (SOTC), Washington, DC, USA 2013. http://stateofthecoast.noaa.gov/glossary.html, (CoaStormEmr - Amer) {881}