The final day of the legislative session is upon us, with a variety of high-profile bills from guns to ethics to education yet to be decided. But legislators already have taken what could become one of their most consequential actions this year.

And it’s not even a law.

HR 4 is a resolution calling for the settlement of something that, at least until recently, you probably believed was settled long ago: the Georgia-Tennessee border.

Turns out, HR 4 is the 10th such resolution our General Assembly has passed since 1887 seeking to correct a surveyor’s error in marking the border two centuries ago. This time, however, the Legislature explicitly threatens legal action if Tennessee will not resolve the dispute with us by the end of next year’s legislative session.

You can practically hear the guffaws ringing through national news stories about HR 4. To read some of them, you’d think even a meth-addled Don Quixote would know better than to accept this quest.

I, too, originally was skeptical about the wisdom of waging a 21st-century fight about a 19th-century mistake. But the resolution does not propose anything as unlikely as annexing a 1-mile strip of Tennessee. Rather, we are only asking for a piece of land wide enough to give us access to the Tennessee River at Nickajack Lake. Which we were supposed to be able to do when the border was established, at least on paper.

Water, or a lack thereof, is one of metro Atlanta’s most critical challenges for the future. Even if we adopt strict conservation measures, build new reservoirs and settle our dispute with Alabama and Florida over use of Lake Lanier’s waters, metro Atlanta could face a shortage of water within two decades.

The Tennessee Valley Authority in 2004 found the Tennessee River had 1 billion gallons per day of excess capacity. Transferring even a quarter of that amount to metro Atlanta, as TVA envisioned, could extend our ability to meet demand for water by at least a couple of decades more.

Brad Carver, an attorney with Hall Booth Smith and Slover, argues Georgia should be willing to sue Tennessee in the U.S. Supreme Court (the only court with jurisdiction in state-border disputes) because we stand to win.

“We’ll be able to clearly establish our border is the 35th parallel, and it intersects the Tennessee River,” Carver told me recently. The document outlining Georgia’s 1802 cession of its western land to the federal government states Georgia’s border “expressly intersects the Tennessee River,” he said.

As state Sen. Charlie Bethel, R-Dalton, noted during a floor debate Monday, the Georgia-Alabama border established at the same time does not run due north from the Chattahoochee River. Rather, it purposely runs north by northwest on a line that takes it straight to the Tennessee River’s bend at Nickajack.

Likewise, Carver said, the 35th parallel was described as Georgia’s northern border when the state was readmitted to the Union in 1870.

“We establish that. Then the burden shifts to Tennessee to prove Georgia has acquiesced” its claims to the disputed land, he said. “The shortest period of time found acquiescent [by the Supreme Court] was 42 years.”

With 10 resolutions during the past 126 years, none allowing more than 37 years to pass in between, that will be hard for our northern neighbors to prove.

Helping our cause is that Tennessee’s legislature in 1889 and again in 1905 described our border as “gravely in doubt.” In 1974, the U.S. appeals court for the District of Columbia found the border was still in dispute. The Federal Energy Regulatory Commission came to the same conclusion in 1981.

It’s not as if this is the kind of dispute that happened only in the dim ages of the past. As recently as 2003, the high court settled a similar fight between Virginia and Maryland.

Not to take anything away from the other bills that have passed this year or may yet pass, but HR 4 could surpass them all if it helps solve a dispute from the past and answer a question hanging over our future.