Probable Scaup
A single female-type Scaup was present this morning, and although it didn't allow for the closest approach, it did perform reasonably well in not very good lighting conditions.
It may be a Scaup, but could also be a possible hybrid. There is some hint of a peaked head on some of the photos, although it does have a good-looking bill and white blaze.
Scaup , 1/2500 sec, f/7.1, 500 mm, ISO 640 (view full size image)