Bioluminescent Algae

Among the animals who emit bioluminescence, you'll find fireflies, glowworms and even some kinds of mushrooms. But one of the most interesting kinds is the pyrocystis fusiformis, an algae that is responsible for the Red Tide effect and glows only when disturbed. Sometimes they'll flash when they're being eaten by fish and krill and such (I don't know what eats them) to draw larger fish to eat their attackers. SCIENCE! Unfortunately, the concentrations are usually so low that's it's almost just a faint blue flash in the water. Sometimes though, you'll get lucky.

That was taped off a bay in Australia when some sharp fellows decided to start throwing water... in the water. Good job guys. Also, the greatest thing you could do would be to drive a motorboat through there in the dark. It would leave like a tail or something.