Immersion Diuresis: Why You Urge to Pee While Swimming
Being submerged in cooler water triggers immersion diuresis, where blood shifts toward the chest, triggering the kidneys to reduce antidiuretic hormone and increase atrial natriuretic factor, causing more urine production to balance fluid volume. That explains the mid–swim urge to pee for most swimmers; it’s a normal, usually harmless reflex and not about absorbing pool water. There’s no reliable way to prevent it, and pool-goers often cope by choosing to hold or go, a behavior widely acknowledged in swimming culture.