There are four stages of cold water immersion.
- Stage 1 or initial “cold shock” happens in the first three to five minutes. Cold shock can cause immediate and involuntary gasping, hyperventilation, panic, and vertigo. All of these can cause water inhalation and drowning. Immersion also can cause sudden changes in blood pressure, heart rate, and heart rhythm. These also can cause death.
- Stage 2 or short-term “swim failure” happens three to 30 minutes after immersion. During this stage, the person loses muscle strength and control. Even normally strong swimmers can lose the strength to pull themselves out of the water or keep their head above water. This can lead to drowning.