How do I get an outside line? http://rulertube.fun ruler tube Near the top of that chain is Lake Lanier, an impoundment of the Chattahoochee River and Atlanta's main water supply. But the U.S. Army Corps of Engineers has numerous reservoirs used for both drinking water and recreation along the Chattahoochee and Flint rivers. The lower half of the Chattahoochee also serves as the border between Georgia and Alabama, bringing another upstream state into the equation.