One morning I looked out at the pond and noticed a hump of brown grass. Then I noticed it moved. Upon closer examination (and some sadly taken photos) I identified it as a nutria - kind of like a beaver with a rat tail.
Sorry the pix are not better, but it was really hard to get closer to him. If I made too much movement, he'd slip into the water and I'd have to wait for him to resurface to try again.
He only stuck around a couple of days. I think the dogs were too much for his nerves. He probably continued his travels along the creek.
Spotting him was a treat, though, as I'd never seen a nutria before, just read about them as being notorious destroyers of water vegetation.