Goosander & mystery ducks

Walking around Cromwell Bottom this morning with Les Midgley we spotted a female Goosander just below the weir on the river section between North Bank and Tag Loop. We also spotted 4 ducks which Les did not recognise but thinks are perhaps some hybrid Mallards. Might be worth someone else checking these out to confirm exactly what they are. We spotted two of the birds feeding in an almost "Shoveler" like fashion in the shallows and then as we walked further along spotted another two weird looking ducks which are completely different in plumage. Eventually all four birds were swimming and feeding together so we assumed they were two pairs ?