The Controversy
A major source of controversy is establishing where the ball last crossed the hazard, not where the ball entered the water, which could be relevant in situations in which where a ball lands on the ground, then rolls back into the water.
The easiest way to deal with this type of problem is to determine the point where the ball was last on, or over, dry land, before it crossed the hazard. Next, determine if the point is between the red or yellow stakes. If it is, you can decide on the best course of action from that spot.
The additional dropping option for a lateral water hazard, however, Atlanta golf courses means that the ball can sometimes be dropped on either side of the hazard, as long as it is within two club lengths of where the ball crossed the edge of the hazard and no closer to the hole. That can make a difference when you finally determine where to drop the ball.