Scientists are predicting a advance-file Gulf of Mexico "ineffective zone" where the water holds too limited oxygen to preserve marine existence.
By posing a significant threat to regional marine life, the pollution that causes the gulf dead zone jeopardizes the tens of billions of dollars generated by commercial fishing in the area.
The 2019 forecast is close to the record size of 8,776 square miles set in 2017 and larger than the five-year average measured size of 5,770 square miles.
US scientists on Monday warned that because of runoff from human activities-such as urbanization and agriculture-this summer's "dead zone" in the Gulf of Mexico is forecast to be one of the worst on record.
"A major factor contributing to the large dead zone this year is the abnormally high amount of spring rainfall in many parts of the Mississippi River watershed", the agency said in its annual "dead zone" forecast.
Scientists had said earlier that widespread flooding made a large dead zone likely this year.
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This year, the low-oxygen area is likely to cover about 7,800 square miles - roughly the size of Massachusetts, NOAA said.
Low oxygen conditions began to appear 50 years ago when agricultural practices intensified in the Midwest, and there have been no reductions in the nitrate load from the Mississippi River to the Gulf of Mexico in recent decades.
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.
We need to create and use more ecologically friendly fertilizers so that when this flooding happens, it doesn't take it to the Gulf to create these dead zones in the first place.
A rush of spring rain feeding into the MS is what's expected to push 2019's zone to a near-record size. She and her team have been monitoring the Mississippi River discharge and nutrient levels since the first big pulse of flood water in the spring, so they "weren't necessarily surprised" by the results of their models.
An oxygen-starved hypoxic zone, commonly called a dead zone and shown in red, forms each summer in the Gulf of Mexico. The partnership included teams of researchers at U-M, Louisiana State University, William & Mary's Virginia Institute of Marine Science, North Carolina State University, Dalhousie University and the USGS.