A search of Douglas harbour and a section of the river flowing into it was completed with nothing found.
The operation was launched early this morning after a member of the public reported hearing shouts for help in the area of the Isle of Man Business School.
The Douglas Coastguard Rescue Team was sent to help police and fire officers.
A team from the Fire and Rescue Service carried out a search of the river, and the marina was searched using an inflatable dinghy, the harbour patrol vessel and teams in immersion suits.
The Coastguard team stood down at 11.15am.
(Picture: Fire officers searching the River Douglas, near the Tesco store, this morning).