Its clear that first bird is one for quiz modus (arent we just fooled by this before? At least I was). Picture quality with strong haze conditions produce this, I think.
First impression was: its a Velvet Scooter (or a Common pochard?), and then I looked for reasons:
-on first sight, I thought that the bill just seems to bend up slightly near the tip, resulting in a Velvet Scooter-jizz (I hope its understandable). But this may be an illusion, created by pixelated picture.
- I thought, the rear end is somewhat drawn-out and the tail looked to long for a Common Pochard, so better for a Velvet Scooter with a concav head-bill profile. But this cant be judged with confidence here.
-a Velvet Scooter has a thicker neck than a Common pochard, that broadens towards the breast. This can be obvious when neck is stretched.
These three points can result in an jizz-friendly body-shape that makes a Velvet Scooter stand out in a mixed flock of diving ducks (and yes, most a larger than Tufted Ducks or Common Pochards). And I thought, these three points are visible here (neck-shape seems not so good for a Velvet Scooter, not thick enough but I am unsure: is the right neck-shape there or not?)
Conclusion? Maybe its better to leave it unidentified, (or better: I learn from others here!), but I wouldnt dismiss the possibility that this is a Velvet Scooter.
Scaup or Tufted Duck can be ruled out with confidence here, but the other mentioned Ducks are a possibility, when taken picture quality into account, but the feeling, that it might be a Velvet Scooter hasnt gone. Or is it a Common Pochard? I cant decide!