Officers responded to reports of a man drowning about 3.40pm and were unable to revive him.

Police said there were no suspicious circumstances surrounding the man's death but a post mortem would be conducted as part of the investigation.

They asked witnesses who have not yet spoken with police to call 131444 and provide contact details for follow up by investigators.

Witnesses can also contact Crime Stoppers on 1800 333 000, or via the Crime Stoppers ACT website.