Look, there are boats in the picture, there could be another one past the light pole, obscured by the trees. Maybe tied up to the low level docks you can see to the right of the light pole.

Someone on the dock or in a boat behind the tree shot a flare gun out towards the water. The streak across the picture is an artifact because the flare was so bright.

Now the real question is whether there was another flare shot from the grassy knoll?