Edited by DiamondSwan - 12/15/15 at 1:29pm
Did you run your finger over the bottom feeling for a splinter? I can't see any blk scab do you see one. Any cuts that you can see? what about trauma like jumping out of the pool or off of something onto a hard surface? Your on the right track with soaking his foot a couple times a day also.
How long have you been soaking? if there is infection you may need to put him on an antibiotic. I really don't like to say use an antibiotic especially since we don't know what is going on. But is the foot feel hot? feel both feet so you can tell normal skin and if this one that is swollen is hot and how hot. Usually heat mean there is a good chance there is an infection going on. Is there any chance you can take your duck to a vet? How is he acti ng other wise ? eating good can he walk at all? another thing you will want to do is keep him from over using his foot right now. Can you take a pic with out the red light being on? it distorts the pic.
@DiamondSwan I'm thinking he has an infection is it possible to see a vet? if not then I think an antibiotic might be in order you don't want this to spread. keep up the soaks also. Poor thing it looks painful. what antibiotics do you have available? or could something have bitten him? spider or snake? look at that foot real close for any sign of a puncture . Lets see if we can get @casportpony to give an idea on what antibiotics would be used for this. Also get a pic of bottom of foot in natural light like the one you posted please. Looking again at the pic could the toe be broken or do you think it's just distorted because of swelling?