PORTLAND,MAINE—The water wars trial pitting Florida against Georgia over an “equitable apportionment” of water from the Chattahoochee and Flint rivers wrapped up Thursday, a critical juncture in the nearly three-decade-long legal battle between neighboring states that could have an immense impact on metro Atlanta.

Ralph Lancaster Jr., the special master appointed by the U.S. Supreme Court to settle the intractable interstate dispute, will now determine whether Georgia must get by on less water. Or he may simply decide that Florida didn’t prove its case.

Florida seeks a cap on Georgia’s overall water consumption, as well as a 40 percent increase in the amount of water flowing into the state from Georgia.

Lancaster, as he has repeatedly done the past two years, implored attorneys for both states to negotiate a fair water-sharing deal. Or else.

“Finally, please settle this blasted thing,” he said after the last witness had finished testifying in the bankruptcy courtroom up the hill from Portland’s bustling harbor. “I can guarantee at least one of you will be unhappy with my recommendation and, perhaps, both of you. You can’t both be winners. But you can both be losers.”

Lancaster said he will promptly, perhaps by Christmas, issue his ruling. Then it’s up to the nation’s highest court to determine the economic, agricultural and environmental future of the Apalachicola-Chattahoochee-Flint river basin.

Any ruling that goes against Georgia could cause huge harm to the state’s economy — as much as $18 billion, according to one estimate.

But Florida, which sued Georgia three years ago claiming upstream hoarding of rivers and aquifers almost killed its oyster industry, bears a heavy legal burden. It was not clear during five weeks of trial whether the Sunshine State succeeded in denting Georgia’s defense that Florida’s troubles were either self-inflicted or due to Mother Nature.

Lancaster will accept post-trial briefs, or summaries, from the two states before finalizing a decision. Attorneys may then have another opportunity to challenge his ruling before the master submits his decision to the Supreme Court. The nation’s high court will likely rule in 2017.

“I suspect Judge Lancaster’s report will be harsh on both Florida and Georgia,” said Ryan Rowberry, a Georgia State University professor who worked on a previous Georgia v. Florida water case. “I reckon he’ll say Florida does suffer some economic loss due to upstream uses in Georgia and, at the same time, Florida can do more to conserve water. And Georgia farmers need to implement some wide-ranging conservation measures as well.”

If the long, litigious and tortuous water wars history — which also includes Alabama and a passel of federal agencies — is any indication, the battle between Georgia and Florida will likely continue well into the future.

The U.S. Army Corps of Engineers, which controls the flow of the Chattahoochee via five dams and reservoirs stretching from Lake Lanier to the Florida line, has yet to weigh in on the case. The agency’s engineers are set to finish a management plan for the river within three weeks. Patrick Robbins, a corps spokesman, declined to comment Thursday, adding the agency “will need to see what the final court decision is.”

Congress could ultimately weigh in on the special master’s ruling by challenging the corps’ water-sharing plan. If, as expected, the special master orders Georgia, Florida and Alabama to create a regionwide water-sharing “compact,” then legislators could again play a role.

Florida, in its 2013 lawsuit, claimed Georgia hoarded water during the 2011-12 drought to the detriment of oysters and endangered fish and mussels in the Apalachicola River basin. The oyster industry collapsed, dwindling in 2014 to $4.4 million in dockside value — a pittance compared with earlier hauls.

A series of scientists Thursday gave lie to Florida’s contention that Georgia’s over consumption of water during the drought caused the oyster industry’s demise. Romuald Lipcius, an oyster expert at the College of William and Mary, said there was no evidence “that low river flows… caused the baywide collapse of the oyster population.” He added, instead, that “unsustainable harvest” measures — over fishing, particularly of undersized oysters, insufficient closure of threatened oyster beds and too little oversight of marauding oystermen — were largely to blame.

Earlier in the day two University of Florida scientists who extensively studied the oyster’s collapse claimed that their research was questioned and their jobs threatened when their findings didn’t jibe with the state’s legal strategy against Georgia. Bill Pine, in a series of emails introduced as evidence, claimed that one of the state’s lead attorneys said he’d “make things difficult for you” if Pine published an oyster report. He considered it a “veiled threat.”

Philip Perry, Florida’s lead trial attorney, declined to comment Thursday.

Well before the trial started, Florida was in trouble. The corps’ draft operating plan for the Chattahoochee, released a year ago, allows metro Atlanta to nearly double the amount of water taken from the river and Lake Lanier by 2040. The agency also concluded that increased withdrawals would have a “negligible” impact on Apalachicola Bay’s economy and ecology.

The U.S. Fish and Wildlife Service has also determined that the corps’ plan won’t “jeopardize the continued existence of the Gulf sturgeon, fat three ridge, purple bank climber and Chipola slabshell” mussels or their Florida habitats.

In addition, metro Atlanta claims great progress on water conservation — at least a 30 percent reduction in per-capita consumption since 2000.

Much of the past month of testimony focused on water consumed by southwest Georgia farmers and whether the Flint River and underlying aquifers were being sucked dry to irrigate crops. The attention prompted Gov. Nathan Deal to warn earlier this week that a court-imposed water reduction would be a “disaster for agriculture.”

Chris Manganiello, the water policy director for the Chattahoochee Riverkeeper, fears the special master’s decision could inequitably affect Georgia.

“I hope that any requirement to send more water to Florida is a burden that falls on the shoulders of all Georgians, not just the farmers in the lower Chattahoochee or Flint rivers which have been frequent targets in this case,” he said after trial.