This is a DUKW kind of duck truck.
It was invented by a different Roderick, Roderick Stephens, for use in World War II.
You can read more about it at various links such as http://en.wikipedia.org/wiki/DUKW
This particular one is at Stone Mountain, Georgia, USA
I drove the one in Branson, Missouri out on the lake and got a Duck Pilots License.
You can inflate and deflate the tires while you're driving. (Deflate the tires for driving on sandy beaches and increase the pressure for normal roads)