ATV + Jetski = Quadski.

What do you get when you cross an all-terrain vehicle (ATV) with a jetski? You get an amphibious quadbike/ATV called the Quadski!

The Quadski represents the third demonstration of Gibbs' HSA technology, following in the tire tracks of its Aquada and Humdinga vehicles. The Quadski is capable of travelling up to 50 mph on land and water and makes the transition, according to the company, at the flick of a switch.

CNET Article | Gibbs Technologies Website