James Creamer, right, and Victor Causey on an oyster reef in Apalachicola Bay. (Mark Wallheiser/For The Washington Post)

A divided Supreme Court on Wednesday gave Florida another chance to prove it deserves more water from its upstream neighbor Georgia in a long-running battle between the two states.

They have been fighting for three decades over the waters in the Apalachicola-Chattahoochee-Flint basin, which covers more than 19,600 square miles in three states. The current Supreme Court battle has eaten up a combined $100 million in legal fees.

At stake is whether the flow of water will favor Atlanta and the farmers of southwestern Georgia or the seafood producers of Apalachicola Bay in the Florida Panhandle, who say the environment and their livelihoods have been harmed.

The court sent the case back to a special master who had sided with Georgia.

“The amount of extra water that reaches the Apalachicola may significantly redress the economic and ecological harm that Florida has suffered,” Justice Stephen G. Breyer wrote for a five-member majority. “Further findings, however, are needed.”

He wrote for Chief Justice John G. Roberts Jr. and Justices Anthony M. Kennedy, Ruth Bader Ginsburg and Sonia Sotomayor.

Justice Clarence Thomas wrote a dissent joined by Justices Samuel A. Alito Jr., Elena Kagan and Neil M. Gorsuch.

Thomas said that Florida had not shown extra water would cure its environmental ills and that even if it would, the cost-benefit factor favored Georgia.

The cap on water use by Georgia envisioned by its neighbor could cost $191 million to $2 billion, Thomas wrote.

“This harm dwarfs the value of Florida’s entire fishing industry in Apalachicola Bay, which produces annual revenues of $11.7 million,” he wrote. “And it greatly outweighs the value of the additional oysters that a cap on Georgia’s use might produce — i.e., no more than a few hundred thousand dollars.”

The Chattahoochee River flows from north of Atlanta, and there are five federal dams controlled by the U.S. Army Corps of Engineers that provide flood control, hydropower and recreation, as well as drinking water for the nearly 6 million residents of metro Atlanta.

The Flint flows from a spring near Hartsfield-Jackson Atlanta International Airport and sweeps through southwestern Georgia, where farmers depend on irrigation for growing ­cotton, corn, soybeans, peanuts and pecans, among other crops in a more than $4 billion industry.

The two rivers converge at the state border to become the Apalachicola, which runs for 106 miles to the Apalachicola Bay. Its wide flood plain through the Florida Panhandle serves as a spawning ground for crabs and gulf fish, and the bay once accounted for 90 percent of the oysters produced in Florida.

Florida has sued to impose consumption caps on Georgia, saying the reduced flow of the water, especially during droughts, has harmed its ecosystem.

Ralph I. Lancaster Jr., a special master appointed by the Supreme Court to study the issue, agreed Florida had been harmed. But he ruled that the Corps of Engineers controls the flow of water and that Florida had not met its obligation to show that the caps it would impose in Georgia would actually benefit Florida.

Lancaster, of Maine, reasoned that when the water is most needed — during drought conditions — the Corps of Engineers would be more likely to store the water in its reservoirs than to send it down to Florida.

The case is Florida v. Georgia.