Right so I'd normally be the first person here saying "drone mate, go back to bed" but hovering over water is the one thing that always makes me stop and think twice. Water and weird sightings go together way too often to be coincidence - lakes, rivers, reservoirs, there's something about it. Could be connected to underground water sources and ley lines if you want to go down that rabbit hole.
What colour was it and did it make any noise? Those two things will rule out about 80% of explanations straight away. Also how long did it hover before it moved or disappeared?
Post any photos or video if you've got them, even blurry ones are worth sharing because sometimes other people spot details you missed yourself.