` ` Dead zones '' lack enough oxygen to support marine life . They are caused by agricultural waste and sewage flowing into sea . Sweden has plan to pump oxygen into Baltic Sea -- world 's largest dead zone . See also : Australia to create marine parks . Some say it 's a distraction from the need to fight pollution .
` ` Dead zones '' lack enough oxygen to support marine life . They are caused by agricultural waste and sewage flowing into sea . Sweden has plan to pump oxygen into Baltic Sea -- world 's largest dead zone . Some say it 's a distraction from the need to fight pollution .