The first clue that it is a shark, is your right leg is missing.
I live in Colorado. Not much chance of encountering either.
listen for the theme music
You made a joke!
Usually dolphins are in groups (called pods?) and surface a lot... you'll most likely see them in the distance... though if you or they get closer, they will go under longer and you might not know where they are. Sharks (from the little I've seen) are normally all by themselves and normally aren't surfacing much at any point. But I haven't seen sharks as often.
unless you were someone who knows about them ..you don't...id just swim my ass of you shore with one hand on my balls and hope I made it