Happened on a beautiful clear day. Calm water, glassy surface and great visibility. Passed through a squall on the way out but other than that nothing. About 35 minutes into a 50/50 dive we were making ascent an the down line began to dance. Looked up and saw lightning hit the surface nearby several times. Didn’t feel a thing but noticed the fish reacted to the thunderclap. Felt that, like a concussive wave, not too hard though. Captain on the boat said later storm boiled up right on top of us out of nowhere. Extended our time on the deco stop hang line but all was good. Waited until the sun peeked out again to surface and remount the boat. Everything went right back to predive conditions with just a a little more wave action on the surface.