My god, it's full of swans

There is one open pond at the Metro Zoo, all through the winter. I don't know what they do to keep it open; if they were heating it I would expect it to steam a lot more than it does. This is four of the flock of resident and overwintering trumpeter swans, along with some miscellaneous ducks.
Resident swans have yellow plastic wing numbers, and leg bands; the wild ones have neither. It's hard to tell which is which with confidence when they're in the water, but I think these are all wild overwintering examples. (Anyone claiming a truly wild bird would find its own pond, and disdain the Zoo's grain bin, is invited to try a short course of winter survival.)