I was there on Sunday too - lots of great ducks! I agree with Bet and will just add a little additional info...You are mostly correct with your photo, but I do not see any scaup. You have 2 Ring-necked Ducks, the obvious male in the left bottom corner but there is a female too on the right side. Look for the brown duck with the pointed head, white around her eye and white ring on her bill. There are 2 Gadwalls, one on the left, one centre front - look for gray/brown ducks with white wing patch. The ducks that you might be mistaking for scaup are 4 female Redheads. Look for plain brown ducks with two-toned head. Lastly are 2 American Wigeon and 5 male Redheads. There were both types of scaup throughout the park so you may have seen them too, as well as several Canvasback. Maybe you have more species in other photos!
Kris