Even on the surface of the ocean, in the presence of other mammals, we are not safe:

13-year-old NSW boy was knocked out and suffered a broken collarbone after a humpback whale swept its tail across the boat he was on.
Draw Hall, from Maclean near Grafton in the northern NSW, was fishing with his parents near Brooms Head on Sunday morning when a pod surfaced nearby.
One of the mammals lifted its tail and swept it over the five-metre long boat from bow to stern, hitting Drew, The Daily Examiner reported today.