Michael Phelps never stood a chance in a race against a great white shark - here's why

On Sunday night, "Shark Week" viewers were disappointed to find out that swimmer Michael Phelps, sometimes called the greatest Olympian of all time, did not actually race against a great white shark.

Instead, Phelps raced against a simulation of a shark, using a special swimsuit with a large fin to help him move through the water at superhuman speeds.

Even with the help of that monofin, though, Phelps lost to the shark by two seconds.

That's because great whites are really, really fast. They can speed through the water at 25 miles per hour (mph), potentially achieving 35 mph for the short bursts. That allows them to propel their entire bodies out of the water.

Even top Olympians like Phelps are unlikely to surpass 6 mph while swimming in the conventional way.

For the "race," Phelps swam 100 meters alone in chilly open water off the coast of South Africa. Viewers watched a simulation of a shark swim alongside him. Discovery producers calculated that shark's speed by towing a seal-shaped decoy in front of a real white shark for 100 meters, and measuring the shark's time. The ocean swimmer came in at 36.1 seconds, just over 6 mph. 

Great white sharks often go much faster than that, of course, but the producers of Discovery Channel's "Shark Week" pointed out that the sharks don't usually keep their speeds up for distances as long as 100 meters.

Under the conditions set for the race, Phelps did pretty well: He beat the world record for the 100m freestyle (set without special gear) by about 10 seconds. Of course, his monofin made a big difference. 

Phelps says he's down to race again.

Although many fans were disappointed that they didn't get to watch Phelps race a real shark, none of us should really want to watch him attempt that. Such a race might end badly, as evidenced by this Discovery video showing a determined shark chasing down a decoy.

Of course, if Phelps really wanted a challenge, marine biologist Andrew Nosal suggested he take on the fastest shark out there, the mako, which can leave great whites behind in its wake.