Emergency services scoured the Tay at Dundee for much of the weekend after reports of a man in the water.
Thick fog was a constant opponent for Coastguard, Police and RNLI units who descended upon the river on Saturday afternoon.
A second day of searching concluded yesterday without success. Recovery efforts are expected to resume today.
Police Scotland first received reports of man entering the water near to the Tay Road Bridge shortly after 4pm on Saturday.
The Broughty Ferry Lifeboat was scrambled and launches from the RNLI station were also detailed to search an area between the V&A construction site and Tesco on the Riverside.
A short time later, they were joined by the Coastguard helicopter and throughout the afternoon the search area slowly widened to take in a stretch of water from Dundee Port to Dundee Airport.
Spotters with binoculars were situated on the bridge and along the shoreline to direct the search, which continued until haar and poor light brought it to a halt.
At one stage onlookers saw a flare in the water and as red smoke billowed, helicopter, lifeboat and launch all briefly converged, opposite Dundee airport.
Just as swiftly, however, they split again and began once more to sweep the river, back and forward in an ultimately fruitless search.
The Coastguard helicopter left shortly after to refuel before returning to make use of the last few moments of light.
On Sunday, however, it was grounded at its base in the north of Scotland by thick fog.
The Broughty Ferry lifeboat continued its search of the water, but crews were hampered throughout the day by the same concealing mirk.
Police Scotland said it was continuing to carry out inquiries and assist in the ongoing search.
A spokesman said: “Emergency services were alerted to a report of a member of the public, believed to be a man, entering the river Tay at around 4.20pm on Saturday.”