UPDATE FEBRUARY 2009: The web site and phone number for Arizona Ducks are not operational. I assume they are no longer in business.
The vehicle isn't really a quack quack duck, its a DUKW. The DUKW is an amphibious 2.5 ton vehicle that was used in WWII, primarily to carry supplies. It is pronounced "duck."
The vehicle used by Arizona Ducks for tours at Lake Pleasant was basically the skeleton of an original DUKW that was rebuilt over the course of a few years by the owner of Arizona Ducks, Brian Hauser, and a few associates. When Brian conducts the tour, you can tell how proud he is of that vehicle! Arizona Ducks is obtaining a second vehicle to be used at various events around town.