Hippos are semi-aquatic megafauna whose welfare in captivity depends critically on access to deep water for thermoregulation, buoyancy, and social behaviour expression.
Hippo welfare in captivity centres on water provision as a fundamental physiological requirement, not merely a behavioural enrichment. Hippos are physiologically adapted to an aquatic lifestyle: their skin lacks sweat glands and desiccates rapidly without regular water immersion, causing cracking and bacterial infection. The secretion they produce, often called blood sweat, provides some UV and antimicrobial protection but cannot substitute for water immersion in managing thermoregulation. Water also provides buoyancy that reduces stress on the hippo's massive skeleton - animals that spend extended periods on land may develop joint problems from bearing their full body weight continuously. Social welfare in hippos requires careful management: the territorial aggression of dominant bulls can cause serious injury to subordinate animals in confined spaces with limited escape routes. High-quality hippo welfare requires deep pools (minimum 1-2 metres) large enough for social groups, separate management capability to reduce aggression injuries, and appropriate haul-out areas with shade for time out of water. The growing recognition that large megafauna welfare requires space and environmental complexity far beyond what traditional zoo exhibits provide is driving improvements across the zoo industry.