Great Northern Diver close to the Cardiff Yacht club moorings c.10:00 (seen from the Barrage side but not seen later on around midday from the boardwalk). Also male Goosander (female seen yesterday afternoon). Lesser Scaup and an odd hybrid (perhaps TuftedxPochard?) also on the reserve.
A couple of record shots of the hybrid on CBWR this morning (Lesser Scaup in the background of the shot on right).
Glamorgan Bird Club 
That’s rather smart and I suspect you’re right about the parentage.