U.S. 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.

The National Oceanic and Atmospheric Administration (NOAA) estimated the dead zone will span 7,829 square miles while Nancy Rabalais, a marine ecologist at Louisiana State University, predicted it will cover 8,717 square miles.

NOAA predicts this summer’s Gulf of Mexico #DeadZone – an area of low-to-no oxygen that can kill fish & other marine life – to be 'very large' ... about 7,829 sq. miles (roughly the size of Massachusetts). More: https://t.co/Jtzgw4zQ0f @noaaocean — NOAA (@NOAA) June 10, 2019

"These numbers are far above the five-year average of about 6,000 square miles," the Washington Post reported. The largest gulf dead zone ever recorded—8,776 square miles—occurred in 2017.

The gulf dead zone is primarily the result of nutrient pollution. The Mississippi River system carries nitrogen and phosphorus from cities and farms to the gulf, where the nutrients fuel an overgrowth of algae. The algae die, sink, decompose, and deplete the water of oxygen, which many marine creatures require for survival.

"When the oxygen is below two parts per million, any shrimp, crabs, and fish that can swim away, will swim away," Rabalais told National Geographic. "The animals in the sediment [that can't swim away] can be close to annihilated."

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.

"It's just a major punch in the gut," Ryan Bradley, a fifth-generation commercial fisherman from Mississippi, told the Post. Bradley plans to travel to Washington, D.C. this month to ask federal lawmakers to declare a disaster in the region, which would open up relief funding for local fisheries.

Today is the day for the 2019 Gulf of Mexico #deadzone prediction. It’s a sad fact that every June, teams of academic & federal government scientists tell us how much of the Gulf will likely be uninhabitable by fish and other sea life later in the summer. THREAD pic.twitter.com/wOj2pJ34cK — Karen Perry Stillerman (@KarenStillerman) June 10, 2019

Dead zones occur across the globe, though the annual one in the gulf is considered among the world's biggest. Experts partly credited the "abnormally high amount of spring rainfall" in the U.S. Midwest this year—which caused catastrophic flooding that could have a notable impact on both farmers and food prices in the long term—for the alarming new gulf dead zone forecasts.

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"While this year's zone will be larger than usual because of the flooding, the long-term trend is still not changing," explained University of Michigan aquatic ecologist Don Scavia, who contributed to NOAA's analysis. "The bottom line is that we will never reach the dead zone reduction target of 1,900 square miles until more serious actions are taken to reduce the loss of Midwest fertilizers into the Mississippi River system."

This dead zone in the Gulf of Mexico is predicted to be the second-largest on record this summer, scientists say. https://t.co/LNUNoqKB8F pic.twitter.com/BofCTt6cUX — USA TODAY (@USATODAY) June 10, 2019

Experts—including David Scheurer, a NOAA scientist who studies dead zones—are also worried that the human-caused climate crisis could exacerbate oxygen level issues in the gulf.

"That is a long-term concern," he told National Geographic. "If the climate does change in that region, there is a fair amount of evidence suggesting you would expect things to get worse."

The magazine reported: