When I first spotted this bird in the water on Tuesday at Occoquan Bay National Wildlife Refuge, I thought it might be a Northern Shoveler, because of the enlarged shape of its bill. I zoomed in with my long 150-600mm telephoto lens to try to confirm the identification and decided that it instead looked more like an immature male Lesser Scaup (Aythya affinis) with some kind of mollusk or snail in its mouth.
According to the Cornell Lab of Ornithology website, “Lesser Scaup eat primarily aquatic invertebrates such as mollusks, insects, and crustaceans, but they also eat aquatic plants and seeds.” However, I am not very good at distinguishing Greater Scaups from Lesser Scaups and immature birds make identification even harder, so I am not all that confident that I have correctly identified this bird.
As you can tell from the photo, the it was windy and the water was quite rough that day, so the birds on the bay were bobbing up and down. I decided not to crop this image any closer in order to give you a sense of the choppiness of the water.
© Michael Q. Powell. All rights reserved.
Mike Powell 
I agree with your identification, that is probably a Scaup. But I can see how you would think it’s a Shoveler from far away.
What a cool and unique waterfowl!