While in the water, do not attempt to swim unless to reach nearby safety. Unnecessary swimming increases the rate of body heat loss. Keep your head out of the water as much as possible. This will increase your survival time.
The body loses heat in five ways: Respiration, Evaporation, Conduction, Radiation and Convection.
Respiration: Heat escapes when air is exhaled. This can be reduced by covering the mouth and nose area with wool or a bandana.
Evaporation: Perspiration evaporates from the skin and moisture from the lungs contributes to heat loss by the body. Control the amount of evaporation by wearing clothing that can be ventilated or taken off. Wear clothing that will not absorb water but will breathe, so you can control the cooling effect of evaporation.
Conduction: Sitting on the ground or snow, touching cold equipment or being rained upon are all examples of how heat can be lost through conduction. If you become wet a large amount of body heat is lost rapidly. Perspiration or rain should never be allowed to saturate your clothing as this can reduce their insulating values. Wear clothing that will keep you warm even if it is wet, such as wool, or some of the new synthetic materials such as polypropylene, polorguard, fiberfill, or quallofil. These all have good wet characteristics. Sit or sleep on a closed-cell insulating pad.
Radiation: Radiation causes the largest heat loss from uncovered skin, particularly the head, neck, and hands. It is important in keeping warm to cover these areas, preventing further heat loss.
Convection: The primary function of clothing is to keep a layer of warm air next to the skin, but to allow water vapor (perspiration) to pass outward. The body continually warms this layer of air close to the body.
Heat is lost rapidly with the slightest breeze unless you wear a nylon or gortex shell over your clothing to prevent the warm air from being lost. The cooling effect of wind chill is due to increased evaporation and convection heat loss. You must have wind protection and good insulating value (dead air space) in order for your clothing to retain your body heat at a safe level.
Frostnip or frostbite is sometimes also present in hypothermia cases. Frostnip is the freezing of the top layers of skin tissue and is most typically seen on cheeks, earlobes, fingers, and toes.
The skin is white and waxy looking. The top layer feels hard but the deeper tissue is still soft.
Re-warm the area gently, generally by blowing warm air on it or placing the area against a warm body part (partner's stomach or armpit). Do not rub the area as this can damage the affected tissue by having ice crystals tear the cell.
With frostbite the skin is white and has a hard feel all the way through with numbness and possible anesthesia. Deep frostbite can include freezing of muscle and or bone. It is very difficult to re-warm the appendage without some damage occurring.
Superficial frostbite may be re-warmed as frostnip if only a small area is involved. If frostbite is severe medical attention is obviously required.
Do not re-warm severe frostbite if you cannot guarantee that the tissue will stay warm, as refreezing after re-warming causes extensive tissue damage and may result in loss of tissue.
There are no absolute rules but in general it is better to move for a few hours with frozen feet to a place of safety than to thaw the feet out in the wilderness.