Looks like fun. Cross an all-terrain vehicle (ATV) with a jetski and you get an amphibious quadbike/ATV called the "Quadski". [em]
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.[/em]
From [a href="vny!://www.gibbstech.co.uk/"]Gibbs Technology[/a]. They also make some modified ones for the military that look truly bad-ass.