Abnormally heavy rains and flooding along the Mississippi River will likely cause a larger-than-normal dead zone in the Gulf of Mexico this summer. Dead zones occur where there is so little oxygen that marine life caught in it can die and it happens every year in the Gulf. They are caused when an excess of nutrients from human activities, like farming, flood into the oceans and create an algae bloom, which in turn creates a dead zone when the algae die and suck the oxygen out of the water as they decompose. Scientists estimate this year’s dead zone will be about 7,800 square miles.