The silent threat of fluid accumulating in your lungs while swimming

Health · Published 18 October 2026 Swipe more like this →

In short: It starts with a sudden cough and shortness of breath, yet no water was swallowed. Swimming-induced pulmonary edema (SIPE) is a rare but potentially life-threatening condition where blood leaks into the lung's airspaces, often triggered by the simple act of exercising in cold water.

SIPE occurs when fluid moves from pulmonary capillaries into the alveoli, causing acute respiratory distress. Unlike drowning, this happens without water aspiration. Symptoms typically include a distressing cough, often producing frothy or blood-tinged pink sputum, and breathing difficulties that seem disproportionate to the physical effort being exerted. In some cases, divers may even experience confusion or irrational behavior. Physical signs can include crackles or a rattling sensation deep within the chest. In some instances, the sensation of wearing a wetsuit may even feel as though it is restricting the swimmer's ability to breathe.

The underlying mechanism is driven by physiological shifts during cold-water immersion. As the body reacts to the cold, peripheral vasoconstriction redistributes blood from the limbs to the chest. This increases central blood volume and raises pulmonary artery pressures. When combined with the high cardiac output of strenuous exercise, the increased hydrostatic pressure in the capillaries may cause 'stress failure,' allowing fluid, proteins, and even red blood cells to leak into the lung tissue. This process is often accompanied by an increase in central venous pressure and pulmonary arterial wedge pressure. In some cases, the fluid leakage includes increased levels of albumin and immunoglobulin G.

While the exact causes remain incompletely understood, several risk factors have been identified. Research suggests a moderate association with water temperatures ranging from 13°C to 23°C. Clinical studies have linked the condition to female sex, older age, hypertension, and pre-existing heart disease. Recent data from large-scale swimming events also suggest that asthma and a lack of recent open-water swimming experience may increase vulnerability. While the condition can be serious, many cases, such as a reported 58-year-old triathlete, show complete resolution within 24 hours of medical intervention. Additionally, recent studies indicate that having a recent respiratory tract infection is a strong indicator of risk. Some researchers have even noted that the condition can be associated with increased heart mass or thicker left ventricular walls.

General information, not professional advice. Spotted an error? Flag the card or see corrections and complaints.

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