<P> Dead zones are hypoxic ( low - oxygen ) areas in the world 's oceans and large lakes , caused by `` excessive nutrient pollution from human activities coupled with other factors that deplete the oxygen required to support most marine life in bottom and near - bottom water . ( NOAA ) '' . In the 1970s oceanographers began noting increased instances of dead zones . These occur near inhabited coastlines , where aquatic life is most concentrated . ( The vast middle portions of the oceans , which naturally have little life , are not considered `` dead zones '' . ) </P>
what causes a dead zone in the ocean
excessive nutrient pollution from human activities coupled with other factors that deplete the oxygen