When the core temperature drops below 90 F serious complications begin to develop. Survival in cold water depends on many factors. The temperature of the water is only one. Others include body size, fat, and activity in the water. Large people cool slower than small people.
Fat people cool slower that thin people.
Children cool faster than adults. By swimming or treading water, a person will cool about 35 percent faster than if remaining still. This technique reduces survival time by nearly one-half in cold water. This survival time can be increased considerably by getting as far out of the water as possible and covering the head. Getting into or onto anything that floats can save a life.