19/08/2026
Hippos can stay under water for about five minutes at a time.
They manage this using sealed facial valves, a slow heart rate, and an automatic reflex that lets them surface for air while staying completely asleep.
*Sealed Features:*
Valves snap shut over their nostrils and ears the moment they dive to block out water.
*Heart rate control:*
Their hearts automatically slow down during a dive to save oxygen.
*Underwater sleeping reflex:*
A subconscious trigger pushes them to bob up for a breath and sink back down without waking up.
*Walking, not swimming* :
Hippos are too dense to float, so they sink and bounce along the riverbed instead of swimming.