Hippopotamuses spend up to 16 hours per day in water in the wild. Providing adequate aquatic environments in captivity is the most critical welfare requirement for this species.
Hippo welfare depends fundamentally on water access quality. A hippo kept in a shallow pool that does not allow full submersion cannot thermoregulate, sleep normally, or express natural social behaviours. Skin dehydration in dry conditions is both uncomfortable and a disease risk - the reddish 'blood sweat' that hippos secrete is a natural skin moisturiser and sunscreen, not an indicator of distress, but it requires water to function effectively. Modern hippo facilities with deep, heated pools, naturalistic substrates and appropriate social groupings achieve dramatically better welfare outcomes than older concrete facilities.