One of the major reasons why humans are afraid of sharks is obvious: We can’t see underwater, and a shark can come seemingly out of nowhere. While around thirty species are known to have attacked humans, in the United States, shark attacks average about sixteen per year, with around one fatality every two years (around the world, shark attacks number around fifty to seventy per year). In one study, the researchers found that most shark attacks occur near shore, which is not surprising since most people who enter the water stay close to the shore. Some researchers believe that shark attacks on humans will only increase over time, as more people live—and play—along ocean coastlines.