NEW ORLEANS (WGNO) — Scientists released findings showing that the Gulf dead zone west of the Mississippi River is smaller than last year, at around 4,772 square miles.

The dead zone is an area of low to no oxygen that can kill fish and marine life. Its size fluctuates throughout the year. Last year, according to their 2024 study, the western dead zone was over 6,700 square miles.

Nancy Rabalais, a professor in the Department of Oceanography and Coastal Sciences at LSU, focuses her research on the Gulf dead zone and the organisms that live in the sediments on the seabed.

Rabalais said the dead zone forms as a result of nutrients like nitrogen and phosphorous that get funneled from the Mississippi River from agricultural runoff. These nutrients fuel the growth of phytoplankton, which are single-celled plants. When they die, they float down to the bottom waters, and in the decomposition, oxygen is used up.

The low oxygen area is usually in the lower-half of the water column or toward the bottom. Rabalais said there's usually enough oxygen in the higher parts to support typical marine life. She said organisms have to migrate into other areas or move higher in the water column, which is not normally where they live. She said this can expose them to higher rates of predation.

The size of the dead zone varies throughout the year and from year to year. It's size depends on the amount of freshwater discharged into the Gulf and the amount of nitrogen and phosphorous in the water.

"It didn't use to be as prevalent and severe as it is now, especially since the 1970s it's more prevalent and it's more severe towards the bottom than it was historically and that has to do with the increase in the nitrogen and the phosphorous that's delivered to the gulf from the watershed," Rabalais said.

The nitrogen and phosphorous increase is related to agricultural farmland and crops. The soil releases nitrogen and phosphorous but farmers also use them in their fertilizers. The excess runoff falls into the Mississippi river and reaches the gulf.

Rabalais said there are times of the year where there are fewer fish in the area than there would be if the dead zone wasn't present. She said it's difficult to pinpoint if the dead zone is causing issues for the fishing industry, since there's so many other factors involved, but she said it could be a factor.

Rabalais said in order to fix the problem, the amount of nitrogen and phosphorous that reaches the gulf needs to be reduced. This is primarily a city wastewater and agricultural fertilizer issue.

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