I was diving along the south side on the palm Beach Inlet back in the 90"s (incoming/slack tide) and was always on the watch for the big ships coming through dragging anchors or crap or the new boat owners who didn't know what a dive flag was.
Needless to say I had my encounters with wolf packs of barracuda's, sharks and the such but it always expected so no big deal. One day I was collecting some fish for my tank and I saw a big shadow go over me and I thought crap don't they see my drive flag, then it occurred to me that there was no motor noise so as I looked up there were about 10 big ass manatees above me with one in my face about a foot or two a way. Not sure why but that almost made me soil my wet suit for a second, caught me by surprise those sneaky bastards. I recovered in a few seconds and petted them and they followed me for a while and left.