I looked that concept a few years ago and decided it simply would not work on a year around basis. I live on Lake Coeur d’Alene and contemplated an amphibian to travel between the TriCities in Washington State. 3 hours by car and 1 hour by air. The problem is the wakes and boat traffic in the summer makes landing on the lake a real challenge and would require some kind of lift to get the plane out of the water so it wouldn’t be beaten to death from the wakes. Just to give you an idea, I spent over $10K in fiberglass repairs to my sailboat and over $3500 in dock repairs, all from excessive wakes. In the winter, very light boat traffic but the usual fog/low ceiling and ice on the water. The lake no longer freezes over but there can be a lot of ice close into shore and in shallow bays. I ended up buying a land based aircraft and used that for commuting. Funny thing is door to door, I saved maybe 1/2 hr but it was way more fun.