Punkalouver - unless you know the beach well, your assessment of shallow water depth is likely to be wrong - when helicopters enter the water they usually, as mechpowi says, roll over. Imagine a successful forced landing to the water and then being trapped upside down in a sinking helicopter - rather a lot of people have sadly died that way.
I, like others, have been trained for underwater escape and the first time you do it, it makes you realise that without training or specialist equipment (STASS) you probably won't get out.
If you have a choice then the beach is the better option