Scaly leg mites are really hard to get rid of, and they do not die off in freezing weather. Fastest way is to dose your birds with ivermectin, but that means egg withdrawal.
If you don't want to buy something, you can use the old fashioned method of dipping each bird's leg into oil (any kind of cooking oil will do) and do it every other day for a couple of weeks. Otherwise, coat legs with bag balm, nustock, vaseline, vet-r-x, etc - what you are doing is smothering the mites.
If you have some birds with the mites, and others not yet affected, treat all - but the ones that don't have it yet you can dip/rub just once a week instead of continuously.
I don't know whether waterfowl can get them or not, but would bet they could, although perhaps not so likely with the continual submerging in water?
Here is someone recommending a lot of different options, including gasoline on the legs. (not sure I would do that one) http://www.the-chicken-chick.com/2013/03/scaly-leg-mites-in-chickens.html