The parents of Toronto filmmaker and conservationist Rob Stewart say they aren’t giving up hope in their search for their son.
Stewart, 37, was reported missing just after 5 p.m. Tuesday after a diving excursion near Alligator Reef in the Florida Keys.
“It doesn’t look great, but we got to believe that he is the type of person who will survive,” said father Brian Stewart.
Stewart’s mother, Sandy Stewart, said the U.S. Coast Guard is leading the search and rescue.
“He’s super fit and he’s a great swimmer and he’s done thousands of dives,” she said.
“They said he’s good to be out in the ocean for 72 hours.”
WATCH: Family asks for public’s help in search for missing Toronto filmmaker Rob Stewart. Erica Vella reports.
Stewart is best known for his award-winning 2006 documentary Sharkwater, a film that explores the hunting of sharks and the destruction of ocean ecosystems.
Speaking with ET Canada, MacLeod said Stewart, an experienced diver, was using a new rebreathing system and was diving “deeper than he’s gone before.”
MacLeod, who was relaying information from a friend, Brock, who was with Stewart at the time, explained that Stewart indicated he was OK once he surfaced but a third diver with the team had apparently “blacked out.”
“Brock had to jump in to try and stop that guy from sinking and he was going under the boat, so Brock pulled him back on the boat apparently by the time he got him back on the boat…Rob was gone,” MacLeod said.
Lieutenant Commander Ryan Kelley from the U.S. Coast Guard said rescuers were dispatched after receiving a call for a missing diver from a crew member of the vessel Pisces.
“Our teams are currently assessing survivability and that takes into account water temperature, as well as individuals height and weight,” said Kelley.
“Right now it’s a search a rescue effort and we are going to do everything we can to find Mr. Stewart.”
MacLeod said Stewart has been in Florida shooting the documentary’s sequel, Sharkwater 2.
“In his eyes, it’s been getting harder and harder to find sharks and get to sharks and he wants to show people new sharks.”
In December, Stewart made an appeal on his Facebook page, asking experienced scuba divers to join him for 300-ft. dives in Florida for his upcoming film.
On Tuesday evening, Stewart’s sister, Alexandra, issued an urgent plea on Facebook for help locating her brother.
WATCH: Sister of missing filmmaker, Rob Stewart, calls brother inspirational
“HELP NEAR ISLAMORADA. FLORIDA – PLEASE HELP WITH A SEARCH AND RESCUE FOR ROB STEWART WHO IS LOST DIVING,” she wrote.
Early Wednesday, Alexandra pleaded for assistance in the search.
“We need and will pay for a small, low flying/slow airplane (preferable) or a helicopter to search this afternoon from about 2pm-4:45pm or as late as 6:15pm,” she wrote.
A GoFundMe page was also set up early Wednesday.
“Rob Stewart was scuba diving on the queen of Nassau wreck, six miles off shore of Islamorada Florida, when he disappeared after surfacing,” reads a statement on the page. “He was last seen at the surface of the water at 5pm from the dive boat. Search and rescue / coast guard is looking but we need all the help we can get / every boat and diver to put all resources into this search.
“We are raising funds to support growing search efforts.”
An update on the GoFundMe page said that searchers secured the assistance of five helicopters and three planes throughout the day.
WATCH: Rob Stewart, best known for his documentary “Sharkwater,” went missing while scuba diving in the Florida Keys.
Paul Watson, Canadian environmentalist and founder of the Sea Shepherd Conservation Society (SSCS), said in a Facebook statement that Stewart and another diver surfaced from the water while using rebreathers.
According to Watson, one diver passed out after boarding the boat.
“As the boat crew pulled the one diver from the water, they turned to retrieve Rob but he was no longer in sight – he had surfaced, so the boat crew thought that he passed out as well, and floated off,” Watson said on Facebook.
The Greenpeace co-founder said the SSCS launched a new vessel in Miami on Tuesday and the Sea Sheppard ship wasn’t able to contribute to the search.
“The Coast Guard is now covering with two vessels and a helicopter equipped with night vision and thermal detection technology.”
“At this point, we can only hope for the best,” Watson said on Facebook.
However, Watson later said on Wednesday afternoon that SSCS’ new vessel John Paul DeJoria had been dispatched to aid in the search for Stewart.
“I spoke with the U.S. Coast Guard. They said they were making an intensive effort and advised that we not enter the primary search area but agreed that we can search to the north of the area where Rob was last seen,” Watson said. “The John Paul DeJoria will coordinate rescue operations with the United States Coast Guard and the USCG Charles Sexton.”
Stewart is a former Sea Shepherd crew member and the SSCS worked with the filmmaker in 2002 to produce Sharkwater, Watson said.