A Man Tosses Water into a River, and Something Underwater Goes Absolutely Nuts

There's video out of Florida of a man who tosses water from a bucket into a river . . . and when it makes contact something underwater goes nuts. 

Whatever the heck it is, it never surfaces so it's almost like some underwater creature from a cheesy B-movie.  Some people think it's manatees, others say tarpons, Andy thinks it’s just another reason never to go in the water.