He was staying near Wiseman's Ferry with friends and family.
Locals, police, the SES and a rescue helicopter were unable to make any progress, before divers were called in.
Investigators say the man was with his two boys and two others, and were riding on a tinnie prior to the incident.
Once the group returned to the boat, the man dived out to swim the remaining 20m.
After making it to the ladder of the housebat, he went under the water again and never returned.
Police will now prepare a coroner's report.
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