Searches have been carried out this week for the 77-year-old man.
A man was swept into a river and dragged away by the current in front of his wife, his son has said.
Euan Robertson told The Courier his father Struan Robertson was trying to clear a hydro-power device on his estate in Perthshire when he lost his footing and fell into the water amid flooding following heavy rain.
A search operation was launched at about 5pm on Sunday after police received a report of concern for a 77-year-old man seen in the River Tay, near Strathtay.
Police Scotland said specialist resources including a police helicopter and drones were used to search for him on Monday amid “challenging” conditions, with searches continuing on Tuesday and expected to resume on Wednesday.
The incident happened at the Pitcastle estate which Struan Robertson has owned for the past two decades.
His son told The Courier: “He was trying to clear a hydro intake from the Tay. It powers the electricity but it gets clogged up when the water is so high.
“He lost his footing and was swept into the river. The current dragged him away.
“I was in Perth at the time. My mother was with him when it happened.”
Police Scotland said the search was launched after a 77-year-old man was swept into the River Tay, near Strathtay.
A spokesman for the force said: “The incident was reported around 5.30pm on Sunday, and a multi-agency response was set up with partners.”
Weather warnings were in place over much of Scotland at the weekend as the country was battered by heavy rainfall, which caused flooding and led to train cancellations and road closures.
There were still 15 flood warnings and nine flood alerts in place on Wednesday morning.
