Blake Lively is the latest to learn the harsh lesson first hand.
The full length trailer for her upcoming features The Shallows has been unveiled. Lively plays a recently bereaved daughter whose mother has passed away. To escape her troubles and try to find balance in her life again, she decides to hit high waters on this golden stretch of deserted beach. It soon becomes clear why it's not a tourist trap considering the waters are literally swimming with deathly dangers.

The Shallows is out August 12. Swim safe kids.