This summer’s dead zone in the Gulf of Mexico, largely fueled by Midwestern fertilizers, will spread across a near-record area the size of Massachusetts, the National Oceanic and Atmospheric Administration reported.

The summertime zone of low oxygen will be approximately 7,829 square miles. The record was 8,776 square miles in 2017. The five-year average is 5,770 square miles.

The dead zone, known to scientists as hypoxia, occurs when nitrogen from fertilizers, wastes and decaying plant matter feeds algae that consume oxygen when they die. Many of the water quality efforts in the Mississippi River basin, which feeds into the gulf, are as much about addressing the dead zone as they are about trying to make rivers and lakes in the Midwest less green. 

Scientists said heavy rain this spring is likely part of the reason for the predicted size. The Mississippi River was delivering 67% more water than normal in May.