Am I A Mallard ?

Trip to the garden centre today to get tropical fish food and budgie food. ( I know, nothing for the garden ).  Planned to get a wide shot of the fishing pool, as the water seemed fairly still so might get some good reflections.  However, I was distracted by this group of ducks.  The lead duck looks rather like a mallard but so much bigger than all of the other mallards.  It was about the same size as the canada geese.  I have tried to identify it but keep coming back to mallard.  Can anyone help?