The 30-year-old had surfaced during the dive at Largo Bay in Fife and requested more weights but he did not resurface.
Forth Coastguard was alerted to the incident at around 1pm today (Thur) after a member of the public reported someone waving for help on a boat.
Kinghorn RNLI lifeboat as well as coastguard teams from Leven and St Andrews rushed to the scene.
Two people on the boat had also alerted Fife Police to incident. And the Royal Navy Rescue Helicopter R177 was sent to the scene to aid the search teams but no trace of the diver was found.
A Forth Coastguard spokesman said: “After a thorough search in very good weather conditions no sign of the missing diver was found. Forth Coastguard stood down the search units at 3.50pm pending a search by Central Scotland Underwater Search Team.”
