Search underway for 'Sharkwater' filmmaker missing off Florida...

Officials are searching for a Canadian underwater filmmaker who went missing off the Florida Keys while scuba diving Tuesday.

Rob Stewart, 37, was diving with a small group near Alligator Reef off Lower Matecumbe Key, the Miami Herald reports. Stewart's sister told the Herald that he was filming part of his "Sharkwater" documentary series at the site of a shipwreck.

What could have contributed to Stewart’s disappearance was that he and another diver were not using conventional scuba tanks, but rather closed-circulation re-breathing diving equipment, according to the Herald.

Regular scuba equipment is open-air circulated and safer to use when diving, Stewart’s sister told the Herald.

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Late Tuesday afternoon, Stewart and a diver resurfaced from their swim and the diver passed out. Once crews got him onto the boat, Stewart disappeared. Crew members believe Stewart also passed out and then floated away.

The U.S. Coast Guard, Monroe County Sheriff’s Office and the Florida Fish and Wildlife Conservation Commission have conducted a search for Stewart, and it is unclear how long the search will last.

Stewart’s sister said her brother was wearing a buoyancy control device to keep him afloat on the surface, but she doesn’t know if it was fully inflated, the Herald reports.

Friends and family of Stewart have set up a GoFundMe account to help pay for the costs of the search. So far they have raised more than $90,000.