Actually, I watched a documentary on a place, I think in South America, where shark attacks where so frequent that you couldn't swim in the ocean. When they studied it, they found the reef surrounding that place was so degraded and devoid of fish that it was causing the sharks to come in closer and attack whatever they came across.
I think that the sharks were bull sharks. They also studied the behavior of the same kind of sharks in Cuba, which is a similar, but very healthy ecosystem. Found quite a difference in the shark's behavior.
There are always sharks out there and as long as we don't deprive them of their natural food sources, our risks are minimal.