The hippopotamus (Hippopotamus amphibius) is one of Africa’s largest land mammals, spending a significant portion of its day submerged in rivers and lakes. This semi-aquatic lifestyle often raises questions about how quickly these massive animals navigate the water. While many perceive them as powerful swimmers, their movement is actually a unique form of underwater ambulation, unlike conventional swimming.
How Hippos Actually Move in Water
Hippos possess a massive, dense skeletal structure that causes them to sink rather than float, making traditional swimming inefficient. They leverage this high specific gravity, using the riverbed or lake floor as a stable platform for locomotion. Instead of paddling, they engage in underwater walking, often described as “bounding” or “galloping.”
This process involves powerful, coordinated leg movements where the hippo pushes off the bottom, effectively bouncing through the water in a series of strides. The water’s buoyancy reduces the burden of their immense weight, creating a low-gravity environment that facilitates this powerful movement.
This bounding gait would be impossible for such a heavy animal to execute on land. In deeper areas where their feet cannot touch the bottom, they may propel themselves forward with coordinated kicks, but this is less common than their preferred method of ground contact.
Physical Adaptations for a Semi-Aquatic Life
The hippo’s body is adapted for spending up to 16 hours a day submerged. Their eyes, nostrils, and ears are strategically located high on the top of their head, allowing them to remain almost entirely underwater while still breathing and monitoring their surroundings. They can also close their nostrils and fold their ears shut to prevent water from entering when fully submerged.
A specialized clear membrane protects the eyes, enabling the hippo to see clearly underwater. When fully submerged, they can hold their breath for extended periods, typically around five minutes, and can even sleep while intermittently surfacing to breathe without waking.
Their skin is nearly hairless and highly sensitive to drying out, necessitating a constant need for moisture. The skin secretes an oily, reddish-pink substance that was once mistakenly thought to be blood or sweat. This secretion is rich in hipposudoric acid and norhipposudoric acid, which function as a natural, pigmented sunblock and an antiseptic agent.
Comparing Their Speed on Land and in Water
The hippo’s bounding movement in the water is swift but relatively slow compared to its terrestrial speed. When moving along a riverbed, their top underwater speed is estimated to be between 5 and 8 miles per hour (8 to 12 kilometers per hour).
In contrast, the hippo is deceptively fast on land. When threatened or charging, they can reach a top running speed of 19 to 30 miles per hour (30 to 48 kilometers per hour) over short distances. This speed is achieved despite their massive weight, which can exceed 7,700 pounds (3,500 kilograms).
While their underwater ambulation is efficient, the hippo is significantly faster when running on solid ground than when bounding through the water.