Many injuries sustained by surfers are caused by the rocks and corral underwater. In areas that attract massive waves, these objects have proven to be fatal. Wiping out into a reef can knock a surfer unconscious, allowing him to be battered by the waves against the reef. Some surfers have even drowned as a result of being caught against corral by their leash. In fact, many surfers who chase the larger waves won't leash themselves to their surfboards for this reason.