It is believed the man had a mobile phone and a set of ear buds with him, but no wallet or direct identification.
He was dressed in a manner which indicated he may have been out socialising prior to his death, and gardai trying to establish how he entered the water.
Early indications are that his death was tragic or accidental, but gardai are keeping an open mind in their investigation.
The results of the post mortem will likely guide the direction of inquiries.
“Gardaí in Mountjoy are appealing for anyone who may have seen anything unusual in the area to contact Mountjoy Garda station on 01 666 8600, the Garda Confidential line on 1 800 666 111, or any Garda station,” a garda spokesperson said.