They may be no match for Michael Phelps, but a chimp and orangutan have proved to scientists that apes can swim like humans.
The two captive animals were separately filmed ploughing through water using a form of breaststroke.
Most land mammals swim instinctively by paddling their paws. Scientists believe the peculiar swimming style of humans and apes might be the result of life in the trees.
Great apes are not known for their swimming ability, and there have been cases of them drowning in zoos that use water moats to confine them.
Both the apes studied had been raised and cared for by humans in the US. One, a chimpanzee called Cooper, showed off his skills in a swimming pool in Missouri. Not only could he swim, but he enjoyed diving to the bottom of the six-foot deep pool to pick up objects.
“It was very surprising behaviour for an animal that is thought to be very afraid of water,” said researcher Renato Bender, from the University of the Witwatersrand in South Africa.
The orangutan, named Suryia, was filmed at a private zoo in South Carolina swimming freely over a distance of 12 metres.
Both animals used a leg movement similar to the breaststroke “frog kick”, according to a report in the American Journal of Physical Anthropology.
Each had a slightly different style. Cooper moved his hind legs together, but Suryia kicked them out alternately.
While the ‘doggy paddle’ is an instinctive action, human-style breaststroke must be learned, said the scientists. The tree-dwelling ancestors of apes and humans might have lost the instinct to swim, developing other strategies to cross small rivers such as wading upright or using natural bridges.
Cooper was raised from the age of two by an American couple, Jill and Brad James, in Malden, Missouri.
He began his aquatic life by playing in the bath, submerging his head under the water.
Without realising that apes are prone to drowning, Cooper’s owners then allowed him access to the shallow end of their swimming pool.
When the scientists started observing Cooper in August 2010 he was unable to swim. But he had an “almost compulsive tendency” to dip under water with his left hand covering his eyes and nose.
He progressed to diving in the deep part of the pool, assisted by safety ropes. Eventually, he taught himself to stay afloat while swimming.
Suryia was deliberately trained to swim and dive by his owners at The Institute for Greatly Endangered and Rare Species (Tigers), a private zoo in Myrtle Beach, South Carolina.
He demonstrated an ability to swim both under water, with his eyes open, and on the surface of his pool. Like human competitive swimmers, he swam on the water surface with his face immersed.
The scientists wrote: “In the following months after our investigation, Suryia improved his swimming and diving skills.
“He began to swim from the shallow part to the deep part of the pool over a distance of six metres, displaying a more coordinated and efficient swimming pattern.”
Later, he began to swim while holding his head above water for the first time.
In sharp contrast to Cooper and Suryia’s behaviour, most apes flounder around in a flurry of swinging limbs when they find themselves out of their depth in water.
The scientists concluded: “The common opinion that apes are not able to swim due to an anatomical barrier is clearly rejected here.
“Furthermore, we showed that apes are able to submerge and stay under water for 15 seconds or longer.”