Since this thread is a otter info thread, I will post some otter observations from ice and snow country useless to those of you with year-round open water,LOL.
Harsh winters, otter often stop traveling and settle down in a beaver pond full of fish, shiners, suckers, whatever, living in a beaver bank den or old house. Might stay in one spot for weeks until settled snow,warmer weather, breeding urge push them on.
Occasionally, they freeze in and have to wait for a thaw to free them. Most of the time when I have found "wintering" otter, they maintain a way up onto the ice.
A friend of mine owns a series of shiner ponds, some with water level control pipes. Pipes all have screens to keep the shiners in their respective ponds. He decided one winter day to drain the shiners from the largest upper pond into the smaller lower ponds, so he cut a hole through the ice to remove the screen and upright water leveling pipe so the water would drain out through the bottom drainage pipe. Watching to see how many shiners came out through the lower end of the pipe into the next pond, his partner was shocked to see an otter shoot out of the pipe!
Pond was sealed up tight with over a foot of ice. We surmised the otter got in as it was freezing up, living in a beaver bank den from years before when beaver had tried to take over his pond. Weren't many shiners left of the thousands of dollars worth he thought he had in there,LOL!
More open winters, or on big rivers that never fully freeze,they continue to travel as usual.