The setting for this dream was the default group/institution setting, kind of a cross between a short-term academic program and summer camp. I think everyone, including me, was a teenager, although it didn't register as being a change in age.
The only thing I remember very well is that the people in charge were organizing an athletic contest. Apparently this was a tradition for the group, and the centerpiece of the tradition was a long-distance, cold-weather swimming contest. The location was at the edge of a lake or maybe the ocean, in a Scandinavian-like climate. I think it might have been winter to boot--at least it wasn't summery, and the water was very cold.
The adults in charge of the contest were gathering people up to participate, and when they came to me they insinuated that it wasn't a big deal, something they had done for years, and not even all that difficult. I must have signed myself up, because when they came around on subsequent rounds they asked if I was getting ready for the competition. I tried to find out more about it and began to realize that I might not want to do it after all. Every time the sign-up lady came out with another informational tidbit about it it sounded more daunting. I had just assumed that we were supposed to wear swimsuits, but then she mentioned that we should wear at least two swimsuits, and probably socks. I looked down and realized that I was wearing a pea-green competition-style suit over a darker green retro halter suit with shirring. I kind of liked them both, especially the retro one, and wondered vaguely where I had gotten them*.
It had gotten near enough to the race time that people were lining up at the edge of the dock (in all kinds of weird clothing combinations), and I was getting a little apprehensive. The organizer lady came around again, and asked me if I was sure I wanted to compete. I asked what the distance was and she hemmed and hawed, but then said that it would be about an hour and a half of swimming in frigid water. I said, "Oh, in that case I'd better not. I could swim for an hour and a half, but I couldn't compete for an hour and a half." I think I was also wanting to put on some regular clothes by that time, and picturing young competitors dropping off mid-race and sinking slowly to a watery grave. The organizer was fine with my withdrawal, and I thought the staff were displaying a weird and irresponsible mix of cavalier disregard for safety on one hand and a stifling tendency to assume my incapacity on the other.
There was another part of the dream involving a very nifty old house in the middle of the desert that had been converted into a restaurant/museum and was supposedly haunted; and an episode involving rapidly rising floodwater about which I was very unconcerned--but I don't remember much about either.
*oddly, I didn't wonder why I was in good enough shape to be wandering around unselfconsciously in a swimsuit, or swimsuits, as the case may be.