The adult male Surf Scoter with its black plumage and white patches on the nape and forehead is distinctive. Female plumages of the Surf Scoter are similar to female plumages of the other scoters. It can be told from the Black Scoter by it more sloping forehead, and white face patches. The White-winged Scoter has white wing patches, a face that doesn't contrast with the crown, and a smaller bill.
Length and wingspan from: Robbins, C.S., Bruun, B., Zim, H.S., (1966). Birds of North America. New York: Western Publishing Company, Inc.