Looks like a mink to me, but I can't be 100% sure since it is a B&W photo. If it was as dark as it appears, then it was a mink.
Barrybarry is right they are all over the place.
A lot of people don't realize that mink are all over the place because they are so rarely seen. Partially because they are normally nocturnal, and partially because people just aren't observant. But if you fish, and you are jut a little bit observant, you will see them this time of year.
I've even seen them in broad daylight at work at the pond outback. I'm talking about a crowded Cleveland suburb and this used to be a golf course.
BTW, I once saw a bass eat a duckling. Well, I assumed that is what it was. The mother acted as described and also was poking her head under water fussing like crazy. All of the sudden SPLASH, and there was one less. that is when I spotted a couple large bass. Came back that evening and caught a 5 pounder. I didn't check it's stomach.
Once caught a much smaller bass, maybe 3 pounds that had a blackbird in it's gut and fledgling blackbirds are likely about the same size as a duckling.
I put up a duck box in my pond in the woods this year, and already a wood duck used it. Saw a mother with newborn babies on the pond about a week ago. Pond also has snapping turtles. Hoping at least a few of the ducklings make it, but then, one year something got a full grown duck on that pond. I assumed snapping turtle because the pond surface was covered in feathers. Wife wants me to trap the turtles, but they serve a function. I got rid of a couple a few years ago, but there are more. I actually have them in both ponds.