I never saw this sort of thing until I watched UK Top Gear racing a Dune Buggy and a snow mobile across open water. And yeah, the first video the guy is doing fine for a while, but I think his hot dogging got water into the engine and ... pppplt. Seems you're better off going in a straight line.
You won't blow a belt unless its worn and ready to do so. I've done plenty of this. Not those distances but enough to skip a lake. The second video those machines were setup to do what they achieved. Big thing is sealing the clutch and belt so they don't get wet. Belt get wet... the clutch pulley gets wet and down you go.