Air is an insulator, 35 degree weather will cause extreme internal temparatures but 35 degree water allows you to transport all your excess energy to the water.

Air is an insulator, 35 degree weather will cause extreme internal temparatures but 35 degree water allows you to transport all your excess energy to the water. 38 or 40 degree water would be deadly, but I wonder what the air temparature is when it gets that far.