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Anas platyrhynchos
man made lake.
Yes you are correct Marta.It is a molting phase for a Mallard.
I have hardly seen any American Black Ducks yet.Nor a Wood Duck for that matter.
I think is a regular mallard male in molting phase (Anas platyrhynchos) :-)
Alternatively could be the american black duck (Anas rubripes). Is hard to say without seeing the body.