Most of the Sa'ami can probably get away with it first time ~ but the others need to "train for the event" and that's best done by reviewing numerous church rosters to see if an ancestor had a FIN or FEN next to his name somewhere ~ 'cause that really increases the odds of having the right genes.
I did something like this in the Army way back when. They needed a volunteer to go out on the ice, jump up and down, and open up the river for "river crossing training".
The long line of troops I was in literally stepped back ~ just like the cartoons!
I raised my hand (and was quite alone), and the training officer in charge asked me "Did you ever do this before" and I said "Yes ~ many times" ~ which was true.
That wasn't about jumping up and down on the ice ~ that's usually kind of stupid and ruins the day for the others but I understood the question to be about swimming around in icy and ice filled river water on a cold day.
I was out there maybe a half hour or so ~ climbing out on the ice, getting up, jumping on it and breaking it up ~ and then it was over and I swam ashore, dried off, got on my clean fatigues and stood by the fire for the next few hours as everybody else got to jump in and out of the river. There were several hypothermia cases that day ~ it was really cold ~ even a wind.
After that none of the fellows in my training company looked at me the same ~ wasn't just that I'd done something special, but to them something impossible, and it played into the hands of the training cadre besides ~ they all got wet!
My grandfather was born in the arctic cirlce in Norway, grandma was Finnish - I live in FL - go figure. Always loved the cold. I remember working in a restaurant as a teenager - used to take my breaks in the the zero freezer with an icy soda. Walked through the regular freezer, in to the zero freezer and loved to just chill in there. Once we were on a business trip up north, right after a blizzard, the guy next to me was freezing, gave him my coat even though he already had a sweater and his own coat - I was a good bit taller so it fit over his coat just fine. I walked the dozen or so blocks back to the hotel in a polo shirt. Most of the family is still up in the UP of Michigan.