It is easy enough to affix floats to a typical drone's landing gear, and it can be huge fun to land on water, but taking off is the hard part. I won't bore you with the science behind water surface tension, but if you forgot that stuff exists, let me assure you that there's a good chance you'll flip your drone into the water if you cannot take-off nice and straight. That about sums it up, be aware that taking off can be risky, and be smart about waves and other ways water can actually contact your drone, but it is otherwise pretty easy to make a floating drone. Have fun!