Phelps' Shark Week special faces backlash for use of CGI

Michael Phelps tried to make it clear to his fans that he wouldn’t actually be side-by-side racing a great white shark for Discovery Channel’s “Phelps vs. Shark: Great Gold vs Great White,” but when some viewers saw the final product they slammed the show’s use of CGI for the big race.

Phelps “raced” the shark as part of Discovery Channel’s annual Shark Week. He competed in the ocean against a computer-simulated fish based on data on the swimming speed of sharks.

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Some viewers expressed disappointment over the show’s use of CGI.

Meanwhile, some defended the athlete's Shark Week show.

Ahead of the Sunday night event, Phelps told ABC News' "Good Morning America," “We're not in the water at the same exact time. I think that's the one thing we all - we want everyone to know — I was safe, which was number one. I had 12 to 14 divers underneath me when we were doing the race.”

Phelps was outfitted with a wetsuit and a monofin to mimic a shark's powerful tail. He finished the 100 meter race in 38 seconds, two seconds slower than the simulated shark.

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Phelps tweeted Sunday that he'd like a rematch, but in warmer water.

The swimmer earlier told Fox News the challenge was “probably the hardest race I’ve ever had.”