Cold-water immersion is the cause of many boating-related fatalities. The danger increases as water temperature decreases below normal body temperature (98.6 degrees Fahrenheit).
Cold-water immersion follows four stages: starting with cold shock, followed by swimming failure, then hypothermia and finally post-rescue collapse.
Most cold-water drowning fatalities are attributed to the first two stages, not hypothermia. All boaters should wear a life jacket and dress for the water temperature, not the air temperature.
If self-rescue is not possible, start actions to minimize heat loss by remaining as still as possible in the Heat Escape Lessening Position, with your knees drawn up to your chest with your arms grasping them together or simply huddling with your arms around other survivors in a circle. Additional layers of clothing can help you stay afloat by trapping air. Wet clothes will not weigh you down in the water as many people perceive, because water does not weigh more than water.
Find a report on cold-water immersion at http://go.usa.gov/24G3