That depends on a whole list of variables, what kind of shark, where, under what circumstances, how much splashing you were doing, etc. Still, if you could see overhead footage of all the people swimming at the beach and how many sharks there were, swimming amongst them, it might make the hair on the back of your neck stand straight. I saw it from a helicopter at Myrtle beach, SC and it was daunting to say the least! Many people swim with sharks and don't even know they do. The thing is, shore-hugging sharks are looking for particular food which also hugs the shorelines, like seals and sea turtles. When they can see the difference, humans aren't what they are interested in. Oceanic sharks are a different story. Injured animals are among the list of what they are looking for, and just about any kind will do ...including humans. The way humans swim in play, looks to more graceful swimmers, like sharks as if they are injured ...thrashing and kicking about in pain. If you swam in the ocean, the way you do at the beach ...with playful, splashing energy and so on, and on the surface ...you'd likely become lunch.