Phelps Vs Shark has taken home gold for Discovery as Shark Week’s highest-rated telecast ever in key demos.

The July 23 special, in which Olympian Michael Phelps went fin-to-fin with a CGI shark, averaged more than 5 million total viewers, making it the highest-rated Shark Week special ever across P25-54, W25-54, and W18-49. The special also helped propel Discovery to become the No. 1 basic cable network in primetime Sunday night. Across the entire day, Shark Week programming reached more than 15 million total viewers, Discovery says.

The July 23 premiere of Shark Week also was the highest live and on-demand streaming day on Discovery Go. More than 50% of the Discovery GO streams were viewed by 18- to 34-year-olds.

While drawing record ratings, the episode was not without controversy. Discovery and Michael Phelps both defended the special after some viewers reacted angrily, complaining that it wasn’t a real shark and they felt duped by promos for the episode.

Discovery issued the following statement earlier this week in response:

“In Phelps Vs Shark we enlisted world-class scientists to take up the challenge of making the world’s greatest swimmer competitive with a great white,” the network said in a statement to Deadline. “The show took smart science and technology to make the challenge more accessible and fun. All the promotion, interviews and the program itself made clear that the challenge wasn’t a side-by-side race. During Michael’s pre-show promotion, as well as within the first two minutes of Phelps Vs Shark, this message was clear, and we are thrilled with the audience and the engagement around the world.”