I photographed that swan (on the shore between visitor center and dam) 
between 3 and 4 PM. I don't have time to put the photos up until tomorrow. They are 
very grainy, but, as Paul says, they show a broad u-shaped edge between the 
top of the bill and the forehead feathering, indicative as far as I know, of 
Tundra. Rear head and crown shape are somewhat blocky, suggestive of Trumpeter, 
feather edge along the gape seems somewhat in between, certainly not a classic 
Trumpeter shape. Bill also seems short in the photos. This bird, on January 
2nd, suggested a hybrid Trumpling, as Paul says. They have been seen in 
Frederick and Montgomery before.

Dave Czaplak