The Low oxygen areas in the world’s oceans or large lakes where no aquatic life is supported are known as Dead Zones. So, the Dead Zones are formed due to low Oxygen or Hypoxia. As per the first Global Environment Outlook Year Book (2003), there are 146 dead zones in the world’s oceans where marine life could not be supported due to depleted oxygen levels. In 2008, the number rose to 405.
Currently the most notorious dead zone is a 22,126 square kilometre region in the Gulf of Mexico.