A group of more reclusive people swimmin in cold water

An older movie in which some people were swimming in cold water. It seems they were russians (i'm not sure) and more isolated from other people. A 12-year-old girl interacts with one of them.

A group of more reclusive people engage in bizarre activities, swimming in cold water.

what year and genre is the movie?

I am sure you can tell us some more. Were they swimming inside, or outside? Like in a swimming pool, or a natural body of water, what? What were some of the other bizarre activities?

Animated or live action? What year did you see it? If you are not sure give us a range. Specific years, not "when I was a kid". What country were you in when you saw it? Cinema or on TV?

What about the film made you think it was "older"?

You really haven't given us much at all to work with here. There is a hobby where people go swimming in firigid water during the winter. It seems to be just called "cold water swimming"

Was this a fictional story, or like a reality thing where the cast are just filmed trying different bizarre activities?

They swim in a lake or river, and it seems like they tend to avoid the rest of the world.
It is not a sci-fi movie, and I believe it is more than 15-20 years old.

Burnt By The Sun fits some of you points. It's Russian about an eccentric family who's away at a lake cabin/house near a lake/river. The old guy has a young daughter. It's during the Summer and not Winter.