PORTLAND, Maine — A monthlong trial aimed at settling a high-stakes water dispute between Georgia and Florida ended Thursday with a special master imploring both sides to negotiate a settlement.

Special master Ralph Lancaster reminded both parties that there’s much to be lost by booming metropolitan Atlanta or by residents of tiny Apalachicola, Fla.

“Please settle this blasted thing,” Lancaster said. “I can guarantee you that at least one of you is going to be unhappy with my recommendation — and perhaps both of you.”

Florida blames the booming Atlanta metropolitan area and agriculture in Georgia for causing low river flows that have imperiled fisheries in Apalachicola Bay. Georgia contends there’s not enough evidence to support drastic action that could imperil the state’s economy.

The lawsuit played out for a month with dozens of witnesses and hundreds of exhibits in Portland, Maine’s largest city, more than 1,000 miles from the disputed watershed.

Lancaster was appointed by the U.S. Supreme Court to make a recommendation to resolve the matter. The Supreme Court will have the final say in the coming year.

The dispute focuses on the Apalachicola-Chattahoochee-Flint River Basin that straddles the two states and Alabama and has Lake Lanier in its headwaters.

Florida contends Georgia us siphoning away more than its fair share, causing the fresh water flow to dry up, killing endangered mussels, harming tupelo and cypress trees and increasing the salinity of the Apalachicola Bay, causing a die-off of oysters.

Georgia contends that it consumes only a small portion of the water and that there’s no clear and convincing evidence to support restrictions that would imperil its economy and drinking water with the goal of helping a much smaller number of residents in Florida.

Georgia’s attorney, Craig Primis, and Florida’s attorney, Phil Perry, declined to comment after Lancaster implored them to return to the negotiating table.

“You can’t both be winners,” Lancaster told them.

The mild-mannered Lancaster, who wore a bow tie and jacket instead of a judicial robe, praised the attorneys’ hard work before giving them more work to do during the holiday season. He set an aggressive timetable for briefs to be filed within a month before he completes his report.

Lawyers will have an opportunity to weigh in on the special master’s recommendation before the Supreme Court weighs in with its decision.