Michael Phelps, the most successful Olympian of all time, is to race a great white shark as part of the Discovery Channel's Shark Week in July.
The 31-year-old swimmer retired after the Rio Olympics with 23 gold medals to his name. However, despite his achievements in the pool, his comeback race is destined to end in abject failure.
At his peak, Phelps could swim 100m in under 50 seconds - a little more than two metres per second, which equates to five miles per hour.
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While that's a lot faster than most other humans, who usually swim at around 2mph, but it is no match for a great white, which can reach speeds of 25mph.
Phelps would also find himself hopelessly outpaced by crocodiles, penguins, otters and almost every other kind of swimming animal.
But there are still a few of nature's less intimidating creatures he could beat in the pool...
Seahorse
Forget the great white shark, why not take on an animal regarded as an even more efficient killing machine - the seahorse?
Great whites are only successful half the time when hunting, but seahorses register a 90 per cent hit rate. That they prey on tiny crustaceans is neither here nor there.
The dwarf seahorse is the slowest of the 35 species and swims at just 1.5 metres an hour. Phelps would win that race, but it wouldn't be much of a spectacle.
Goldfish
If Phelps wants to race a famous fish, he should choose something everyone is familiar with, such as a goldfish.
"A goldfish can be trained to swim at about 0.86mph," claims website Neatorama. Phelps would beat that easily, notching up another victory for humankind.
But don't dismiss the goldfish out of hand. If they were the same size as Phelps, they would easily win, as they can travel more than four times their body length per second.
Crown of thorns starfish
Starfish are not quite as stationary as you might imagine and the infamous crown of thorns starfish, responsible for destroying coral reefs, is a relatively speedy species.
But these things are relative and they would not be able to trouble Phelps in a race. It would take a crown of thorns almost an hour to travel the length of an Olympic-sized pool, as opposed to 25 seconds for Phelps. Given the amount of time he would have, Phelps might want to stop and cull a few on the way to protect the world's reefs.
Coral
Contrary to popular opinion, corals are invertebrates, not plants. But having said that, they behave very much like plants in that they don't move much. Advantage Phelps.
Sea slugs, often found living around coral reefs, could make a more worthy opponent, but not much.
Sunfish
Finally, a race worth watching. Sunfish are the biggest bony fish in the world and can weigh up to a tonne.
They cover great distances across tropical oceans hunting jellyfish, but they do it very slowly. With a top speed of around 2mph, a sunfish would not be out of place in the medium lane at the local pool and Phelps would have no problem outpacing one.
Tiger
If Phelps is determined to take on an apex predator, his best bet would be to challenge a tiger. Unlike domestic cats, tigers are not afraid of water and are more than happy to take a dip. They're no slouches neither and can reach speeds in excess of 5mph.
If Phelps wants to win - and escape a gruesome fate - he would do well not to race a Bengal tiger, which is so at home in the water it has webbing between its claws.
