One was killed by a shark attack while giving a spear on Fraser Island in Queensland.
The attack happened around 2.30pm on Saturday when a man (3,) from the Sunshine Coast dived from the Indian head east of the island.
He bit his leg and died of his injuries about two and a half hours later, police said.
A physician and nurse provided first aid on the shore before paramedics arrived.
Fraser Coast Mayor George Seymour said the local community was deeply saddened by the tragedy.
“This is a very sad day for our community,” Mr Seymour wrote on Facebook.
“Our deepest condolences go out to the family and friends of this young man.
“A young life with her future in front of her is a tragedy beyond words and we share their grief and sorrow.”
This is the fourth deadly shark attack in Australia this year.
Last month, Gold Pedestrian Gold Pedestrian Rob Pedretti died after being suffocated by a three-meter white shark on Salt Beach in South Kingscliff, North NSW.
A shark killed Zachary Rabba of the Queensland Wildlife Range in April on the northwestern island of the South Great Barrier Reef.
Veteran diver Gary Johnson, 5, was killed in January by a shark off the Cool Island of Esperance off the south coast of Western Australia.
A report will be prepared for the coroner.