otter perhaps

At 3:08:53 pm, I spotted a weasel-like critter on the ice of the millpond. I didn't see how it got there, but as I watched it for the next 61 seconds, it got closer and closer to my vantage point on the waterfall shore. Occasionally, it would come to a stretch of open water, whereupon it would nonchalantly jump in and swim to the next section of ice. Finally, it came to a spot on the ice about 20 feet from the waterfall rocks. Without pause, it entered the cold water, swam to shore, walked along the flat stones towards the waterfall, and then ducked out of sight, perhaps into a crevice, perhaps sliding down the still frozen edge of the falls and into the river. It never resurfaced and it left me very confused about its identity. Because of its ease with swimming, and because I'd seen otter scat and otter footprints in this area, my initial impression was that it had to be the otter I'd been looking for all these years. But it just doesn't fit the field guide description, and almost everyone who's seen the picture has called it a fisher cat. I didn't think they were swimmers, so I'm going to have to call in the experts.