I had a Max 2 amphibious 6x6
It was slow (30mph) but it was fun

I used to have and race a 1988 Honda 250R fourtrax would go about 90 mph in 500 feet and able to skip open water for a distance of 350-400 feet, just like a rock until you slow down then it would sink..gotta hit the water at about 70 mph tho, kind of scary at those speeds... I also had an old ARGO like rig I think it was called a Jigger, Phil's small engine has it now, he is trying to adapt a snowmobile motor into it..