strange flash

[GRADY]

I have seen my share of impacts. I tried to vary the gamma on this image to see if there were any markings in the water around the flash. There is what COULD be called a bow about the flash. This does appear asymmetrical as if the item struck the water at an angle.
The trail does mark an angle that could account for this effect. The fact that the trail is not as clearly shown leads me to think that the item had a shape that prevented the item from being consumed on entry. I would do a debris search and look for any metallic increase in the area. The fact that no effect is shown in the later photo would put the object at a rather small size.

[Janina]

I agree with Grady, it would be wise to search the waters in that area. It looks to me that the flash is behind the pole, and that suggest that something very hot was falling and crated the mist/cloud of vapor.
The splash it may not be visible if the object was very small