Katelyn Weisbrod | August 9, 2018

Scientists found the dead zone in the Gulf of Mexico is smaller this year than in years past.

The zone of water lacking sufficient oxygen to support aquatic life at the end of the Mississippi River measured just over 2,700 square miles — about the size of the state of Delaware and the fourth-smallest the zone has been measured since 1985.

Experts at the National Oceanic and Atmospheric Association expected the dead zone to be more than double this size this year. The lack of oxygen in the water is caused in part by algal blooms stimulated by nutrient runoff from farm fields in states like Iowa into the Mississippi River. Algae deplete dissolved oxygen in the water making survival nearly impossible for fish and other aquatic life.

A possible explanation given by Dr. Nancy Rabalais of Louisiana State University is that winds in the area may have mixed oxygenated water with the water lacking oxygen, reducing the zone’s size.

Scientists from Louisiana State University measure the zone’s reach annually, but the size can vary significantly throughout the year. In 2017, the zone was measured at its largest size ever recorded — over 8,700 square miles. These data help inform efforts like the Iowa Nutrient Reduction Strategy about the progress of such initiatives to keep agricultural runoff and other nutrient loads from entering the Mississippi River.