Here is a navigational oddity that I've been playing with for some time. David Lewis, who is rather famous in Pacific Island navigation circles, reported a phenomenon that is called 'te lapa' or 'underwater lightning'. He reported three Pacific Island navigators who claim to have seen/used this.
According to the reports, on dark, overcast nights, they would see flashes of light leading to islands when they were many nm away from islands that pointed toward islands. There have also been some reports of this by others, although another anthropologist, Rick Feinberg, says he tried, but could not verify it.
There is no real causal mechanism attributed to underwater lightning, but I found the topic difficult to stay away from. The informants went to some lengths to distinguish this underwater lightning from normal bioluminescence kicked up in the wake of a canoe or from waves crashing.
I showed some of these reports to a colleague who specializes in dinoflagellates - single celled organisms that photosynthesize during the day, but give off light at night when hit with a pressure wave. My colleague, Woody Hastings, said he had seen something like this from fish darting. We couldn't really figure out how this might give directional information, but I decided to do a test. I got some dinoflagellate 'starter' from Woody and cultivated 3 liters of the little guys and then poured the concoction into a long trough and pulled a fishing lure through and photographed it to see if it looked like underwater lightning - at least my impression of what it might look like.
Here's a YouTube with it:
