A federal district judge has issued a ruling that creates a significant setback for the state of Georgia in the ongoing water wars among Florida, Georgia and Alabama.

U.S. District Judge Paul Magnuson, from the District of Minnesota, on July 17 ruled Georgia must stop using water from Lake Lanier to meet Atlanta’s drinking-water needs within three years unless Congress permits it. He also ruled withdrawals over the next three years must be frozen at current levels.

Florida Gov. Charlie Crist (R) called the ruling a “monumental milestone....The judge’s decision allows the governors to come together to reach an agreement outside of the court system.”

The ruling is the latest development in an 18-year saga pitting the three states against each other over use of waters in the Apalachicola-Chattahoochee-Flint River Basin. The disputes have focused primarily on the U.S. Army Corps of Engineers’ operation of its four Chattahoochee River dams. The largest is Buford Dam, a 192-ft-high, 2,360-ft-long earthfill structure that forms Lake Lanier, north of Atlanta. Congress authorized its construction to provide flood control, hydropower and navigation improvements.

Atlanta now relies heavily on Lake Lanier for its drinking-water supply, but Florida and Alabama say they also need water from the reservoir for commercial fisheries, farms and municipalities.

The key question in the current case is whether the Corps could lawfully re­allocate water from Lake Lanier for drinking-water purposes under the Water Supply Act, a 1950s-era law that said modifications of certain reservoir projects required congressional approval.

Florida and Alabama argued the Corps was obligated to seek congressional approval to oversee water-supply contracts and install water-intake structures in Lake Lanier because Buford Dam was not authorized as a water-supply project.

“The court recognizes this is a draconian result,” Magnuson wrote in a 97-page ruling. But “The Corps’ failure to seek congressional authorization for the changes it has wrought in the operation of Buford Dam and Lake Lanier is an abuse of discretion and contrary to the clear intent of the Water Supply Act.”

Georgia Gov. Sonny Perdue (R) says he is “deeply disappointed” by the ruling and will appeal. He adds that he plans to look to Congress for assistance in settling the dispute.