Although they spend much of their time in the water, hippopotamuses are one of the few animals unable to swim. Their inability to swim is partially due to their density. Instead, they walk or gallop along the bottom of the river.
The Portuguese man-of-war, a siphonophore that resembles a large jellyfish, is also unable to swim despite residing in water. Instead, the animal drifts with the current in hope of finding food and avoiding predators. The Portuguese man-of-war is capable of adjusting its density to either increase or decrease its depth.
Despite the myth that the giraffe cannot swim, scientific observation has proven that the long-necked animal is capable of floating in water and attempting a type of dog-paddle. Similarly, although popular myth considers the great ape incapable of swimming, great apes who have been raised by and live around humans have been observed swimming, sometimes even learning to enjoy it. While they lost their instinct to swim during the process of evolution, they did not lose the physical capability.
Almost all animals, even those who live in areas without much water, are capable of swimming or of learning to swim. This latent ability is due to evolutionary development and first appeared in terrestrial animals around the Early to Middle Cambrian period.