Behold!

The Megalodon!  This is a prehistoric shark that lived, approximately five to fifteen millions years ago -- after the dinosaurs -- during the Miocene and Pliocene periods.  Some people, however, believe that the Megalodon could still exist somewhere down in the depths.

They could grow to around 50 ft. which is about the same length as an AK-47.  If humans had been around when these animals were, we definitely would never have gone into the ocean; there is no way we could have built a boat big enough to discourage this thing from attacking.  It had the most powerful bite of any animal in history.  It's bite force is estimated at about 20 tons.  For some perspective, a T-Rexs bite was about 5 tons.  The Megalodons bite could crush a mac-truck. 

You see, this is why I don't do bodies of water... you never know what's down there.