The five-year-old was reported missing from a lake in the popular holiday town of Nagambie in central Victoria on Tuesday afternoon.
She was with her family at the time of her disappearance and was later found by a family member.
The scuba diver, aged in his 60s, was pulled unconscious from waters off Swansea at Lake Macquarie in NSW's Hunter Region on Tuesday.
Bystanders tried to help the man before paramedics arrived but he could not be saved.
Surf lifesavers in NSW have performed at least 630 rescues over the break and a call out has been issued for more members to patrol beaches.
There's been 93 rescues in Victoria for the same time period.
NSW Ambulance Inspector Kay Armstrong was particularly concerned about a high number of children getting into trouble and said rivers were extra dangerous because of recent flooding.
"You've got a lot of undercurrents, you've got a lot of other debris in the water," Ms Armstrong said on Wednesday.
"People need to be aware if they can't see the bottom, I probably wouldn't even enter the water."
There's been at least 10 drownings at coastal and inland waterways around Australia over the holiday period and another man was missing as of Wednesday evening.
On Christmas Day, a 19-year-old man died at Lorne in Victoria's southwest and a 36-year-old man in NSW drowned after being pulled from the Hawkesbury River in northwestern Sydney.
On Boxing Day, a man in his 30s was found unresponsive in Lake Hume near the NSW-Victorian border, a 17-year-old boy died near Mordialloc in Melbourne's south and a 73-year-old South Australian woman was found unresponsive in waters at Seacliff, south of Adelaide.
Two teenage girls died in a boating incident in Tamworth in northeastern NSW on Tuesday and body of a 33-year-old Taiwanese man was recovered from a lake near Collie in Western Australia.
A search was also launched on Tuesday for a man missing in the Murrumbidgee River at Wagga Wagga.
Ms Armstrong said it was vital people remained vigilant over the festive season, particularly as some drank more alcohol at this time of year.
"Enjoy yourselves but just be careful, safety doesn't take a holiday."
So far 16 people have drowned in Australia this summer, including six children, according to Royal Lifesaving Australia.
About 145 people died last summer, which which was the worst on record for two decades.
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