It's hardly "contrary to popular belief," since I think anybody with a pulse is aware that the Hughes Hercules (I hate the demeaning term "Spruce Goose") got off the water. But the real question is whether it actually flew or simply flew in ground effect.
The latter involves a perfectly legitimate category of vehicle, for the Soviets made a variety of WIG craft designed to cruise fast over large bodies of water, but people continue to argue whether the Hercules was an airplane or a WIG craft.