White Mallards?

Question

I have just returned from a walk by the river where we saw 2 white ducks. They were swimming happily with normal looking mallards. They were completely white with yellow/orange bills, but otherwise looked like the other mallards. One was with a group on the side of the river nearest us, the other was with another group on the far side. The river is probably more than 50 or 60 feet wide, and we are talking rural not urban. We take this walk almost every day and I have never seen them before. I did notice yesterday a strange looking mallard with a drake. She was there again today. She is mottled brown/white. She seems to be paired up with the drake. 
 In many years walking by this river I have only ever seen mallard ducks. 
 Are these escaped farmyard ducks, or could they be leucistic?

Susan · Answer

I would have thought farmyard ducks, but maybe you need closer investigations

Jimbob · Answer

As well as Susan I would have thought Farmyard... 
 But Mallards are known to interbreed with loads of other Ducks...think it's a wildfowl thing!! 
 There was an Eider/Mallard hybrid up here not that long ago...strange looking individual!! 
 Also saw a picture once of a Swallow crossed with a House martin....weird!

duckwoman · Answer

Hi, I keep domestic ducks which are White campbells, They are originally derived from the mallard and a white pekin duck. They are often seen in the wild as escapees or have been dumped by a previous owner. If they become interbred, they develop coloured patches on the beak and legs. They are slightly larger than mallards but have the same build and shape.