There are many risks associated with voluntary or involuntary human presence in water, which may result in death directly or through drowning asphyxiation. Swimming is both the goal of much voluntary presence and the prime means of regaining land in accidental situations.
Most recorded water deaths fall into these categories:
Panic occurs when an inexperienced swimmer or a non-swimmer becomes mentally overwhelmed by the circumstances of their immersion, leading to sinking and drowning. Occasionally, panic kills through hyperventilation, even in shallow water. Exhaustion can make a person unable to sustain efforts to swim or tread water, often leading to death through drowning. An adult with fully developed and extended lungs has generally positive or at least neutral buoyancy, and can float with modest effort when calm and in still water.
A small child has negative buoyancy and must make a sustained effort to avoid sinking rapidly. Hypothermia, in which a person loses critical core temperature, can lead to unconsciousness or heart failure. Dehydration from prolonged exposure to hypertonic salt water—or, less frequently, salt water aspiration syndrome where inhaled salt water creates foam in the lungs that restricts breathing—can cause loss of physical control or kill directly without actual drowning.
Hypothermia and dehydration also kill directly, without causing drowning, even when the person wears a life vest. Blunt trauma in a fast moving flood or river water can kill a swimmer outright, or lead to their drowning. Adverse effects of swimming can include:
Exostosis, an abnormal bony overgrowth narrowing the ear canal due to frequent, long-term splashing or filling of cold water into the ear canal, also known as surfer's ear Infection from water-borne bacteria, viruses, or parasites Chlorine inhalation (in swimming pools) Heart attacks while swimming (the primary cause of sudden death among triathlon participants, occurring at the rate of 1 to 2 per 100,000 participations.
Adverse encounters with aquatic life: Stings from sea lice, jellyfish, fish, seashells, and some species of coral Puncture wounds caused by crabs, lobsters, sea urchins, zebra mussels, stingrays, flying fish, sea birds, and debris Hemorrhaging bites from fish, marine mammals, and marine reptiles, occasionally resulting from predation Venomous bites from sea snakes and certain species of octopus Electrocution or mild shock from electric eels and electric rays Around any pool area, safety equipment is often important, and is a zoning requirement for most residential pools in the United States.
Supervision by personnel trained in rescue techniques is required at most competitive swimming meets and public pools.
