Swimming with sharks seems possible. I saw one scientist (also in National Geographic) that showed what shark need to bite people according to him. He says they need smell, sound and sight to attack.
So he threw food to bullsharks and went into the water. Now, he says, you see i'm not bitten because they only smell the food but i don't look like it nor do i make sound.
He's surrounded by some 6 or 7 bullsharks at that time. He then proceeds to swim so 2 out of the 3 "needs" are fulfilled. Still he's not attacked since the water there is clear and the sharks see that he isn't prey. He was only bitten once: he did the same as described above but in murky water.
He might have a point. Anyway, some sharks like the white shark are very curious so they tend to bite surfers because of this: recent investigation show that sharks do not attack surfers because they look like prey but just because the shark is curious. But unfortunately for us, a small "nosy" bite of a shark can already provide leathal injuries for us.
But still little accidents happen and they are an encridble species.
I once did some research for a science project way back when i was still in school and they found giant fossile shark teeth. Some sharks must have been the size of whales back then!!!
