This afternoon (3/2) on Potomac River between Violette's and Riley's Locks:

Horned Grebe, 6
Tundra Swan, 12
Other birds included - Red-breasted and Common Merganser, Lesser Scaup, 
Ring-necked Ducks, Bufflehead, Mallards, GBB, Herring and Ring-billed Gulls.

Closer to home at Lake Placid (adjacent to old National Geographic HQ)

Horned Grebe, 1 (my first record there)
Redhead, 2
Lesser Scaup, 1
Buffleheads
Hooded Mergansers
Ring-necked Duck, Mallard, Canadian Geese
American Coot

Andy Martin
Gaithersburg