Smart ass remark: Its -15F here in minnesota, and i went swimming last night…in the pool.
Serious answer: My buddy swam in 61 degree water with nothing but a tri suit for 1 mile, but he is more…insulated than some. Mind you he was the only one in the Oly not wearing a wetsuit, but the sprint people did not wear them for their 1/4mile swim.
Lynne Cox swam 5 miles in 40 degree water from Alask to Russia wearing a bathing suit, cap, and goggles. She’s also swam a mile in waters off Antartica. Scientists have confirmed that she can maintain stable body temperature with her head out of the water in water temperatures as low as 44 Fahrenheit.
I read about another woman, the name escapes me. I think she’s from South America who was attempting an Antarctic swim. She can actually make her body temperature rise for several degrees using meditation before getting in the water.
Extreme examples, sure. Some folks freeze when it dips below 70. It all depends on body fat, temperament, mental focus, etc.