Keep wondering.

This video has been making the rounds on social media and the Interwebs, purporting to be footage of lightning striking a river. The truth is that it's the work of a Finnish engineering company dredging a river. You can see the fuse ignite at the 7-second mark. 

Here's what happens when lightning really does strike a body of water, in this case, the Atlantic Ocean at Daytona Beach, Florida two years ago. Further proof that nature always puts on a better show than a few mere mortals with some firecrackers.