Republican presidential candidate Marco Rubio has dipped a big toe into the exhausting regional battle over water rights that has divided Georgia, Florida and Alabama for more than two decades.

And one high-profile Georgia official is publicly wondering why the U.S. senator from Florida took the plunge.

Rubio joined Florida’s other U.S. senator, Democrat Bill Nelson, and Alabama’s two Republican senators to criticize the U.S. Army Corps of Engineers’ “mismanagement” of the Apalachicola-Chattahoochee-Flint river basin and urged that both states be shielded from any shenanigans in a pending appropriations bill.

The senators want Congress to weigh in on the fight in a forthcoming omnibus spending bill by preventing any changes in water plans by the corps until the states' governors hash out an agreement. The three states have warred over water access since the 1990s, and the latest round of litigation between Florida and Georgia is pending before the U.S. Supreme Court.

The court agreed in November to weigh a maneuver by Florida seeking to limit Georgia’s water withdrawals from the Chattahoochee to 1992 levels. Back then, metro Atlanta’s population hovered around 3 million people. It now surpasses 5.4 million and is expected to grow to 8 million by 2040.

In addition to the fight over the Apalachicola-Chattahoochee-Flint basin, Georgia and Alabama have also squared off over the Alabama-Coosa-Tallapoosa basin.

Both basins played a part in a letter the Alabama and Florida senators wrote to the Senate Appropriations panel overseeing spending on water projects.

“We urge the Subcommittee to include language in any omnibus appropriations vehicle that ensures that management of both of these critical basins are not left to the whims of an unaccountable federal bureaucracy, but instead is properly determined and agreed upon by each state’s governor,” they wrote.

The dispatch raised eyebrows in Georgia. Chris Riley, who is Gov. Nathan Deal’s top aide, took particular exception to it. Referring to Rubio’s letter, he wondered aloud: “And he is asking Georgians to support him for president?”

You will recall that, in June, Deal listed four Republicans he'd be willing to endorse in the 2016 contest. Rubio was not one of them.

The Rubio letter raises the stakes for what had already been a months-long Georgia-Alabama water fight over appropriations language regarding the Alabama-Coosa-Tallapoosa basin, pitting U.S. Sen. Richard Shelby, a Republican from Alabama and a member of the Senate Appropriations Committee, against U.S. Sen. Johnny Isakson, R-Ga. Now the Apalachicola-Chattahoochee-Flint basin and the Florida delegation have entered the mix, with Georgia trying to keep Congress out of it.

Georgia fared well when the corps recently updated its water-sharing plans for the Chattahoochee River, delivering a proposal that would allow metro Atlanta and the state's downstream cities to soak up much more water than they currently use.

It also concluded that the increased withdrawals would have a “negligible” impact on the economy and ecology of Florida’s Apalachicola Bay. That didn’t win any friends in Florida, and Rubio’s letter says Atlanta’s water withdrawals already have “significant negative impacts” on Alabama and Florida.

That echoes Florida’s argument in its current water case against Georgia before the Supreme Court.

The case continues to hit Georgia financially. Deal signed an executive order this week transferring an additional $5 million from his emergency fund to cover the costs of the legal battle.

That's on top of the $4 million he shifted from that account in February to cover the rising courtroom costs. Some statehouse observers predict that Georgia's share of the litigation for this appeal could amount to roughly $20 million.