While on the subject, are float planes ever landed on snow / ice ?
The answer is not no. I am not aware of anyone landing a floatplane on snow. I'm sure it's been done, but would be unwise, as getting it stuck there is a risk. Skiplanes are already easy to get stuck and frozen in, and the skis have plastic non stick bottoms, float bottoms would freeze in much worse! I recall the older version of the Canadian regulations did permit landing floatplanes on snow, as long as passengers were not carried, though this has been removed (probably because it would be unwise anyway, and no wise pilot would do it routinely). I would certainly land a floatplane on snow in an emergency as a preferred surface, though float flying in the winter is less common. It is risky taking off or landing in the water below freezing air temperatures - splash freezes on the plane (ask me how I know!). When flying amphibians over snow, it is a reassuring forced landing surface. When a friend and I flew his 182 amphib across northern Norway in June, all of the snow on the ice cap looked reassuring for a forced landing, compared to doing it on wheels!
Intended landing on snow with any landing gear has another high risk, that being often the surface of the snow is unbroken, and indistinct. Judging your height about the surface for flare is very difficult. There is a specific technique called glassy water landing, which can be applied to snow (ski) flying as well, though is increased risk. You also should have an idea of how deep the snow is. I have purposely landed in 2 feet deep power snow during ski testing, and the plane could not take off out of this. There are tricks for this situation when you're "away", but they are involved and time consuming. I'd done my testing beside a cleared runway, and was on wheel penetration skis, so I just powered over to the runway, and took off there on wheels.
I have landed on floats on ice twice, and was a passenger a third time - ironically once as a passenger, the twenty some years later as the pilot of the same Cessna 185 amphibian - both times due to a right side wheel gear extension failure. The third time, I had had a cross bracing wire break during flight in a 180 straight floatplane, and chose the ice of a frozen lake, rather than the water, in case the plane collapsed on the floats. It did not, and I taxiied on the ice until the plane dropped into the water, and I taxiied to the dock at the floatplane base for repairs.
I would categorize any of the foregoing as abnormal procedures, with a higher risk, avoid if possible!