The area of low oxygen that forms every summer in the northern Gulf of Mexico, fed by fertilizer and runoff flowing down the Mississippi River from the Heartland, is expected to be the largest ever this year because of heavy rains and the river’s high water levels.  

The oxygen-depleted region, called the “dead zone” because marine life struggles to live in it, is predicted to be the size of Lake Erie, or between 8,500 square miles and about 9,400 square miles, according to federal and university scientists.   

The actual size of the dead zone will be measured over the summer.  

The largest recorded dead zone was found in 2002 when 8,400 square miles of the Gulf was found to be lacking in sufficient oxygen for most marine life.