High rivers and high levels of nitrogen and phosphorus from farm and urban runoff mean a larger than average oxygen-starved record from 2017 is nearly 8,800 square miles (22,800 square kilometers).
If there's a tropical storm during the two weeks before the summer measurement cruise, it would stir up the water and reduce the area covered by about 30%, the forecast noted.
Hurricane Barry reduced last year's hypoxic zone, but it was still the eighth-largest on record.
Scavia noted that federal-state plans to reduce the size of the dead zone by reducing runoff pollution have been in place for nearly two decades. "Clearly, something different needs to be done in the watershed to actually reduce the nutrient loads and reduce the size of the dead zone," he said.
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