I can't help thinking that the model for Disney's Donald Duck, was in fact, our tufted duck (Aythya fuligula)! It is a small, compact duck but with a big character. It is a quite distinctive duck too, its white sides being a marked contrast to the dark metallic blue/black of the back and head. Early in the year its breeding crest is clearly visible. The only duck you could confuse this with is the scaup which is a close relative but generally found on salt water, out at sea in bays and estuaries. This photograph is, of course, of the male, the female is very similar but the white is replaced by a less conspicuous buff and the crest is much shorter. The tufted duck is a diving duck, as opposed to a dabbling duck, so it will frequently disappear beneath the surface of the water before popping up again a few feet away from where it originally dived.
Although the tufted duck is widespread it is found almost always on freshwater lakes and ponds as well as slow moving rivers throughout Dorset. It can be seen all year round although it is scarce in August whilst moulting but it is far more common in winter as extra reinforcements arrive from the frozen north.
Large expanses of freshwater are their preferred habitat and Poole Park usually has tufties on the boating lake and they can also be found at Longham Lakes, Hatch Pond, Radipole and Abbotsbury.
Radipole lake is surely the best location to ensure tufted duck goes on your Dorset list.