The insect reacting to the shout is the Water Boatman (Corixidae). The lake has very few, if any, fish in it, so a huge population of water bugs, mostly Corixidae (from what we could see). For whatever reason, the ones that happen to be on the surface when we shout shoot forward rapidly when they hear a loud voice. The ones that are underwater don't react at all. They don't react to a clap. The only thing that got a reaction out of them was shouting. They seemed to prefer "Hey!" You could actually "see" the speed of sound by watching their reaction propagate across the lake.