The Gulf of Mexico's hypoxic zone, or "dead zone," is below average this year, according to the National Oceanic and Atmospheric Administration.
The area of low to no oxygen is 3,058 square miles, compared to last year's zone, which came in at 3,275 square miles.
Measurements are taken from an annual survey cruise during the last week of July. This year, it was led by a team of scientists from Louisiana State University and the Louisiana Universities Marine Consortium aboard the R/V Pelican.
While the size of this year's "dead zone" is below the 37-year average of 5,205 square miles, NOAA officials said almost 2 million acres of habitat could be potentially unavailable to fish and marine life — nearly as much area as Yellowstone National Park.
"Dead zones" are areas that have little to no oxygen — and the Gulf's zone is the largest in the U.S.
"Right now, there's over 300 systems around the U.S. that are impacted by hypoxia, a lot of that has been exasperated by human conditions from nutrient loading," NOAA oceanographer David Scheurer said.
Each spring and summer, the nutrient runoff from fertilizers in the Mississippi River stimulates algae growth once it reaches the gulf. When the algae dies, the decomposition process pulls oxygen from the water, making it unable to support marine life.
"Most organisms will die. And then organisms that are more mobile, they'll end up fleeing the area," Scheurer said. "And that's part of the reason why it's considered a dead zone."
Scheurer said the discharge from the river is a big driver of the hypoxic zone each year.
Marine life exposed to hypoxia have been found to have altered diets, growth rates, and reproduction.
But it also has an economic impact, as some of the effected areas are very productive fishing grounds.
"Those organisms get displaced or they have barriers, and then economically, it also can affect fishermen," Scheurer said. "They might have to travel farther (and) have a harder time finding shrimp or fish to catch."
The five-year average of the dead zone is 4,347 square miles — two times larger than the target of 1,900 square miles by 2035, according to NOAA.
Records for measurements began in 1985. The largest "dead zone" was in 2017 and measured 8,776 square miles.
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