I see. I'm looking right now on https://wiki.openstreetmap.org/wiki/Key:water, and for pond it says " 	A pond: a body of standing water, man-made in most cases, that is usually smaller than a lake." This is the definition I'm using and agree with. I know for reservoir it adds that it is held back by a dam, and while the ponds in this area *are* usually impounded by a small earthen dam, I think the small size takes priority in the definition here. Ivy Lake itself I would probably consider the smallest "reservoir" I would tag. 