I was riding my golf cart on the levee today looking at how high the Mississippi River was and I saw a boy on the river side of the levee, just from the shoulders up, traveling about 15 mph through the water.
As I got ahead of him I could see a pipe sticking up which had to be the air intake and I realized he was on a 4-wheeler traveling silently through the water as the water acted like a muffler for the engine noise.
I never got to see what make it was since it was underwater but it is amazing how those things can travel under those conditions. Wish I had my camera with me.