I believe in the event of a water landing (aka crash) the pilot hits a button and the floatation bags inflate, keeping the aircraft near the top of the water to assist passenger evacuation and rescue efforts. I spot a bottle under the nose that *may* be connected to them to rapidly inflate them as well.
Although being top heavy, don't think for a second that the aircraft is right way up after a ditch (personnel would most likely go through a training exercise in a simulated crash in a pool where you go upside down and practice evacuating underwater).
And then finding a rescue chopper for the rescue chopper would be... interesting
