I earned a pat on the back today, by doing the 30-yard swim to "the rock" in 53-degree river water. I felt good about it because I had stood in the river for several minutes, getting psyched, and entertaining the notion of actually not doing it.
The nice thing about this routine is that the swim forces about a 30-second immersion through a mild river current, involves a little scramble on to the rock (which is warm), then forces me to swim back to shore, so I get two cold-water dips.
The "hazards" of cold-water dips, based on the temperature alone, are greatly exaggerated, and derive from an overly pampered population that spends too much time in artificial environments.
The human body can adapt to both cold-water immersion and hot weather. Ancestral peoples of different cultures have used cold river swims, and hot springs, for health reasons for many centuries. Cold thermogenesis, the fancy, science-y term for swimming or immersion in waters of less than about 68 degrees F., is so good at reducing inflammation and tuning the body, that it's now used as an advanced athletic routine (not just after events, but before them too).
Among other effects, cold immersions spur the recruitment and generation of "brown fat" or brown adipose tissue (BAT). This is a kind of fat, unlike white fat which is a storage tissue, that actually has metabolic activity and burns calories, somewhat like muscle or lean mass. BAT is more vascular, thus explaining the brownish color.
When you become cold adapted, you increase body-heat production via non-shivering thermogenesis, which means you burn more calories at rest by means other than shivering. This is called "adaptive thermogenesis." In other words, don't get FAT get BAT!
I'm going to try to swim the cold river five times per week, and to go as late into the year in Vermont as I can. That's the goal, anyway. The next chapter is to spend at least 15 minutes at a stretch in waters less than 60 degrees.