Identify this waterbird?

The other evening, Tammie and I were walking in Willmore Park, around
one of its ponds, and we saw a bird we didn't recognize. Two of them,
actually, behaving like a courting pair. Both looked similar. They were
ducklike, but had a slightly longer neck and longer legs than the run of
ducks. Their bodies were mostly white with gray wings. Their bills were
duck-like and black, their eyes seemed orange or to have an orange ring
around them (though that may have been reflection of the mercury vapor
lights roundabout), and at least one of them had a swept-back crest on
its head very like the crest of a wood duck. Coloring was all wrong for
a wood duck, though.

All of the above is as accurate as I can get it, given that it was after
dark--though the park is relatively well-lit--and several days have
passed. If it sounds almost like something, let me know. Chris
said they sounded like immature swans, but I don't buy it. Necks too
short, color all wrong, and who ever heard of a crested swan?

Wish I knew where our "identify the birds of missouri by color" book
was.