Hippopotamuses, despite their hefty appearance, are surprisingly agile swimmers. These semi-aquatic mammals can reach impressive speeds in the water, often surprising observers with their agility. On average, a hippo can swim at speeds of around 8 kilometers per hour (5 miles per hour). However, when threatened or during a territorial dispute, hippos can accelerate to even faster speeds, reaching up to 30 kilometers per hour (18.6 miles per hour) in short bursts.

Their streamlined bodies, webbed feet, and buoyant nature aid them in swiftly navigating through water bodies like rivers and lakes. While not as fast as some other aquatic animals, such as dolphins or seals, hippos' swimming abilities are nonetheless impressive given their large size and weight. This adaptation allows them to move swiftly through water to escape predators, defend their territory, or search for food.

So, to directly address your query, "how fast can a hippo swim?" Hippos can swim at speeds averaging around 8 kilometers per hour (5 miles per hour), but they can accelerate to speeds of up to 30 kilometers per hour (18.6 miles per hour) in short bursts, showcasing their remarkable agility in the water.