Hi Quintilia,
long time since I spend my time over the water
but technically speaking, a weight on wheel switch closes, when there is weight on the wheel - hence landing - and opens, when there is no weight on the wheel.
Evenso there is some air in the wheels - I canīt imagine, that that is enogh buoancy, to trigger the switch, when the bird is swimming on its floats.
Greetings Flying Bull