> One thing I hadn't considered before this experiment was that the effort required to swim would help keep me warm. Is that any help in snow melt water? How long till you're shivering uncontrollably?
To rephrase the last question first - how long till you realise what a ghastly mistake you have just made getting in the water? Oh, about as long as it takes for the shock to travel from your skin to your brains.
Mind you, I have seen people go swimming in water with ice bergs -there are so-called 'ice berg' swimming clubs in Northern Europe. But they are mad - and they are NOT in a remote area of wilderness.
> How much do you think body fat or lack thereof affects one's ability to handle said shock?
Most of the 'ice berg' swimmers I have seen were carrying a bit of body fat - rather more than 7% I would say. :-)
> Or is it more a mental toughness issue?
Darn right! There you are, stripped off in the cold wind, and you stick your foot in the water ... Eeeeccchhh!
I helped a party of four males who had swum a very small creek in the snow once. (Incompetent - there was a safe crossing nearby.) Then they travelled a few hundred metres uphill to a hut where we had a fire going. Two of them collapsed for the rest of the afternoon; the other two were in a poor way but standing. VERY dangerous stuff. If we had not been there and had a fire going, their survival rating would have been 'poor'. If the hut had not been there - survival unlikely.
We have waded across a river of snow melt once. We planned it out very carefully in advance.
1) Gaiters off, boots and socks off, trousers off, boots on, arrange clothing and gaiters carefully and strategically around neck. Socks went in zipped trouser pockets.
2) Wade as fast as possible across 10 metres, up to knees, me first.
3) Exit onto bank, throw gaiters down on snow, stand on gaiters (off snow!), grab trousers and dry legs fast.
4) Then, and only then, take pack off and put trousers back on. Wind chill just standing on the bank while wet is a serious factor too.
5) Then dry feet with socks, put socks on, put boots back on. (Nordic ski boots actually - they survived the river crossing quite well.)
6) Finally, help Sue finish dressing as well, pick up packs, and start walking as fast as possible to warm up.
Fun stuff - sort of :-)