megalodon was a prehistoric shark that conservative estimates place at around 16 metres ft) long. For scale, the biggest example of the largest living fish species today -- the whale shark -- was metres ft).
I've swam in the ocean and never been attacked by a shark, however, I was walking in a field and was chased by a cow (there was no calf around either). Gee, thought sharks were aggressive and cows were docile.
And the main reason sharks kill people is because they think your a fish. Also people kill more sharks, than sharks kill people. I can't remember exactly but its like every 1 person a shark kills, we kill like sharks.