STORY: "Without a healthy ocean life, our planet as we know would not exist," Momoa said.
Around 7,000 people, from heads of state to environmental activists, are expected to attend the conference, which was postponed from 2020 to this year due to the coronavirus pandemic.
Dozens of youth activists from various countries clapped and cheered as Momoa, who will soon become the U.N. Environment Programme advocate for Life Below Water, spoke about the problems facing the world's oceans.
"The time now is to act. Our ocean is in trouble. If we combine ambition, dedication and hope we can change the outcomes," said Momoa.
Momoa is known for his role as Arthur Curry, a half-human, half-Atlantean character in DC Comics' Aquaman, which takes viewers to the underwater world of the seven seas. Aquaman 2 is scheduled for release in March 2023.