Why they're dangerous: Unlike most sharks (which live in oceans), these predators are able to swim into rivers, bringing them into closer contact with people than your typical Great White. "You actually get them coming into the canals in Florida," says Wade. "They've been found quite a long way up the Mississippi." And if one happens to swim by you, it could mistake you for a snack. "They might just take a bit of a mouthful, purely exploratory. But what from the shark's point of view is an exploratory nibble, from a person's point of view could be a fatal bite."

How to stay safe: Bull sharks tend to be nocturnal, so avoid swimming early in the morning or late at night. And if you see fish jumping out of the water, be careful. "That means something's chasing them," says Wade, "so don't go in there. It's about understanding this thing that's potentially dangerous. A lot of it's about altering our behavior. You can't expect the [animal] to alter its behavior."