Not sure of the legality of the ATV aspect in NH. Never owned an ATV so not sure what the laws are. But, I sure know places in NH that you could drive an ATV and then go straight into a lake.
One of my many unfulfilled dreams, this albeit from the dot.com era when many of us had more money than sense, was to create an amphibious SUV – and please remember gas was ~$1 gallon then. I came up with some designs. My goal was to have a SUV that you could drive up to Glendale Docks in Guilford with your groceries and then go straight into the lake to your place on an island. Remember, I had a boat-based take out delivery business in those days — Waiters On Water (WoW). That is why I still own www.wownh.com.
These puppies are around $40,000. That is bagatelle for many around here. So I can definitely see them around this Summer. No dealers as yet in NH — and yes, I did, for a second, think about becoming a Quadski Dealer.
It is popular in Russia and they were planning to feature it at the Sochi Winter Olympics next year. Then there was an accident, caught on video, that killed one person and injured another. [Here is a link to the story and video.]
It was this story that piqued my interest, though I think I might have heard about it before. It looks like a load of fun, though I think I am too old. I can just see it at Gunstock. You can use it on grass or on water. Yes, my mind is racing.