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Second, basic geography should tell you that Tennessee would only be one state affected as the Tennessee runs into the Ohio which flows into the Mississippi. Remember the record low levels on the Mississippi last year? Barge traffic was stopped for weeks.
Third, let me assure you, Georgia has an incredibly lousy case. That's why they've never sued. Their only feasible strategy is to try to bluff Tennessee into giving away their water. In order to successfully sue, Georgia would have to come up with a valid legal reason why they haven't sued for 200 years. Georgia has let Tennessee city and county governments be incorporated in the supposedly contested areas. They've built probably hundreds of millions in infrastructure. Tens of thousands of people have lived in those areas, paid Tennessee taxes, voted in Tennessee elections, broken Tennessee laws and have gone to Tennessee jails.
The old common law defense is called laches, sitting on your rights in such a way as to lose them. Here's a more scholarly article in the Tennessee Bar Journal.