From Swamp - "But the ponds I'm thinking about you would most likely lose any miss in the muck before it had a chance to float.... hmmm."
Yup, if the arrow goes in deep enough it has a chance to get caught in weeds and muck, especially with broadheads that offer some snagging resistance. If the arrow is way out there, they are darn hard to spot too, depending on weather & wind conditons. Might help to cap dip arrows with bright colours to aid in recovery. Best of luck with your duck hunting!