Tourists flock to the beaches of North Carolina and Virginia for their safe calm waters. But beneath the serenity of this Atlantic coastline a dark danger is lurking. There have been 2 spikes in shark attacks a decade apart.

Between 2012 and 2013 Maui, Hawaii is rocked by an unprecedented wave of shark attacks, 3 times more than average, leading scientists and state officials to wonder what’s happening, and when the sharks will strike next.

In 2005, shark attacks along the Gulf of Mexico exploded, five times more than the average. The cause is a mystery to locals and experts, and the answer could devastate thousands of miles of American coastline.