Friends said Simon Nelst, 35, was a “water lover” and an experienced diving instructor.
Mr Nelst is believed to be a British immigrant living in the Wally Creek area of Sydney, and was engaged.
Authorities say Mr Nelst was killed by a white shark near Little Bay in East Sydney.
Emergency services were called to Little Bay around 4.35pm local time on Wednesday when a swimmer was reportedly attacked by a shark.
Della Ross, a friend of the victim, was among those who paid tribute.
The victim of the Ravenin Island ‘shark attack’ was identified as Richard, an Edinburgh government employee …
He told Broadcaster 7 News: “Everything connected to Simon is connected to me by the sea.
“The news hit us like a truck because it really is one of the things that makes this land better.”
Eyewitness Chris Linto said the swimmer was in the water when the shark “came and attacked him vertically”.
He told Nine News TV: “We heard a scream and then turned around. It looked like a car had just gotten into the water, a big spray.”
Lucky Frachnan, of New South Wales State Ambulance, said the “victim suffered serious injuries” as a result of the attack, adding that medical staff had nothing when he arrived at the scene.
The incident is believed to be the first fatal shark attack in Sydney since 1963.
Shark attacks are rare in Sydney because of the city’s long-standing nets and other barriers.
The search is also on for the animal responsible, which biologists believe is a white shark at least three meters (9.8 feet) long.
A spokesman for the Department of Primary Industries (DPI) said: “Based on public footage, including eyewitness accounts, DPI shark biologists believe that a white shark is at least three meters long. , Was probably responsible.
“DPI NSW will continue to work with the police and Surf Life Saving NSW to monitor the area and provide technical advice and resources as needed.”
Mr Nelst is believed to have been training for the 5k Malabar Ocean III this weekend when he was killed.
The event has been canceled out of respect, organizers said.