`` Dead zones '' lack enough oxygen to support marine life . Comment: Sweden trialling plan to pump oxygen into Baltic Sea -- world 's largest dead zone . Critics say it 's a distraction from the need to reduce pollution .
`` Dead zones '' lack enough oxygen to support marine life . They are caused by agricultural waste and sewage flowing into sea . Sweden trialling plan to pump oxygen into Baltic Sea -- world 's largest dead zone . Critics say it 's a distraction from the need to reduce pollution .