'Sharkwater' Director Goes Missing, Last Seen Diving Off Florida Keys

— -- Authorities are searching for a Canadian documentary filmmaker who went missing this week while scuba diving near the Florida Keys, the U.S. Coast Guard said Wednesday.

Rob Stewart, 37, the director of the award-winning film "Sharkwater," disappeared Tuesday afternoon as he was working on the film's sequel, "Sharkwater Extinction," his friends told ABC affiliate WPLG-TV.

The Coast Guard immediately launched a massive search mission as soon as they received a report that he was missing, the statement said, noting than members of the Navy, the Florida Fish and Wildlife Conservation Commission and the Monroe County Sheriff’s Office were assisting with the search and rescue efforts.

The Coast Guard said that Stewart was reported missing near Alligator Reef, which is off the coast of Islamorada, Florida.

Stewart's friend, Brock Cahill, told WPLG that at the end of their dive Stewart surfaced and signaled that he was fine, but then vanished.

"I had already been out of all my gear, so I just grabbed a mask and a pair of fins and jumped in the water and started swimming in circles to see if I could find him, but I couldn’t find him," Cahill said.

Tyler Macleod, another friend of Stewart's, pleaded for the public's help in the search effort.

"If you know anyone who could get to Florida, anyone who could get in boats, get underwater, just get there and help the search efforts," Macleod said on "ET Canada."

The filmmaker's mother, Sandy Stewart, told WPLG that her son was a conservationist and passionate about changing the public's perception of sharks.

"It was his mission to change people's perception about the ocean and how we should look after it," Stewart said.

In a 2007 interview with ABC News, Rob Stewart discussed his film "Sharkwater," and his widespread conservation efforts for dwindling shark populations.

"I think if you're in the water with sharks, you should be grateful for the opportunity to meet one," he said at the time. "I think more people who can get underwater with sharks, the better."

The filmmaker's father, Brian Stewart, said that he was heartbroken and trying not to lose hope.

"If God cares, he's going to bring him back to me," Brian Stewart told WPLG.