If this is not followed by an exit to the surface, low oxygen levels and excess carbon dioxide in the blood trigger a neurological state of breathing emergency, which results in increased physical distress and occasional contractions of the vocal folds.

Other contributing factors include the state of the water itself, distance from a solid footing, physical impairment, or prior loss of consciousness.

Even small quantities can cause the extrusion of liquid into the lungs (pulmonary edema) over the following hours; this reduces the ability to exchange the air and can lead to a person "drowning in their own body fluid".

A conscious person will hold their breath (see: Apnea) and will try to access air, often resulting in panic, including rapid body movement.

Both deep and distance free divers often use hyperventilation to flush out carbon dioxide from the lungs to suppress the breathing reflex for longer.

[34] When water enters the larynx or trachea, both conscious and unconscious people experience laryngospasm, in which the vocal cords constrict, sealing the airway.

In most people, the laryngospasm relaxes sometime after unconsciousness due to hypoxia in the larynx, and water can then enter the lungs, causing a "wet drowning".

[37] Comparatively, aspiration of hypertonic seawater draws liquid from the plasma into the alveoli and similarly causes damage to surfactant by disrupting the alveolar-capillary membrane.

[38] Submerging the face in water cooler than about 21 °C (70 °F) triggers the diving reflex, common to air-breathing vertebrates, especially marine mammals such as whales and seals.

Of those who die after plunging into freezing seas, around 20% die within 2 minutes from cold shock (uncontrolled rapid breathing and gasping causing water inhalation, a massive increase in blood pressure and cardiac strain leading to cardiac arrest, and panic), another 50% die within 15 – 30 minutes from cold incapacitation (loss of use and control of limbs and hands for swimming or gripping, as the body 'protectively' shuts down the peripheral muscles of the limbs to protect its core),[43] and exhaustion and unconsciousness cause drowning, claiming the rest within a similar time.

That includes mariners [and] even many (most) rescue professionals: It is impossible to die from hypothermia in cold water unless you are wearing flotation, because without flotation – you won't live long enough to become hypothermic.Submersion into cold water can induce cardiac arrhythmias (abnormal heart rates) in healthy people, sometimes causing strong swimmers to drown.

[46] The physiological effects caused by the diving reflex conflict with the body's cold shock response, which includes a gasp and uncontrollable hyperventilation leading to aspiration of water.

[citation needed] Most people who experience cold-water drowning do not develop hypothermia quickly enough to decrease cerebral metabolism before ischemia and irreversible hypoxia occur.

Indications of drowning are unambiguous and may include bloody froth in the airway, water in the stomach, cerebral edema and petrous or mastoid hemorrhage.

[citation needed] Drowning in saltwater can leave different concentrations of sodium and chloride ions in the left and right chambers of the heart, but they will dissipate if the person survived for some time after the aspiration, or if CPR was attempted,[26] and have been described in other causes of death.

[77] The time a person can safely stay underwater depends on many factors, including energy consumption, number of prior breaths, physical condition, and age.

It is very important to avoid aiming directly at the victim, since even the lightest lifebuoys weight over 2 kilograms, and can stun, injure or even render a person unconscious if they impact on the head.

Victims with suspected serious spinal injuries (which limit the movements) would need special care and specific grips to be ascended properly.

[85] For unconscious people, an in-water resuscitation could increase the chances of survival by a factor of about three, but this procedure requires both medical and swimming skills, and it becomes impractical to send anyone besides the rescuer to execute that task.

[86] However, handling the weight of the body could cost time and efforts in some cases, especially in victims with spinal injury (at the neck or the back) that affected their mobility, which requires special care.

The cardiopulmonary resuscitation (CPR) would follow an 'airway-breathing-circulation' ('ABC') sequence, starting with rescue breaths rather than with compressions as it is typical in cardiac arrest,[88] because the problem is the lack of oxygen.

[92] Methods to expel water from the airway such as abdominal thrusts (Heimlich maneuver) or positioning the head downwards, should be avoided, due to there being no obstruction by solids, and they delay the start of ventilation, and increase the risk of vomiting.

However, in those who are unconscious, it is recommended their temperature not be increased above 34 degrees C.[94] Because of the diving reflex, people submerged in cold water and apparently drowned may revive after a long period of immersion.

[95] Low water temperature can cause ventricular fibrillation, but hypothermia during immersion can also slow the metabolism, allowing longer hypoxia before severe damage occurs.

[104] Some literature suggests that occurrences of drowning can lead to acute kidney injury from lack of blood flow and oxygenation due to shock and global hypoxia.

[114] In the fishing industry, the largest group of drownings is associated with vessel disasters in bad weather, followed by man-overboard incidents and boarding accidents at night, either in foreign ports or under the influence of alcohol.

[114] Scuba diving deaths are estimated at 700 to 800 per year, associated with inadequate training and experience, exhaustion, panic, carelessness, and barotrauma.

[122] Many low-income countries in Africa have the highest rates of drowning, with incidence rates calculated from population-based studies across 15 different countries (Burkina Faso, Côte d'Ivoire, Egypt, Ethiopia, the Gambia, Ghana, Guinea, Kenya, Malawi, Nigeria, Seychelles, South Africa, Uganda, Tanzania, and Zimbabwe) ranging from 0.33 per 100,000 population to 502 per 100,000 population.

[123] Potential risk factors include young age, being male, having to commute across or work on the water (e.g. fishermen), quality and carrying capacity of the boat, and poor weather.

[123] In the United States, drowning is the second leading cause of death (after motor vehicle accidents) in children aged 12 and younger.