Donna O'Halloran took to the freezing Forth in an inflatable dinghy clad in a dry-suit, snorkel and face mask in a bid to put an end to the mystery of her 18-year-old son David's whereabouts.
The Stirling University student vanished on the wintry night of January 19 after a night out clubbing with university friends in the city.
Mrs O'Halloran, whose search proved fruitless, said her hopes were raised of a breakthrough in the case during yesterday's seach after she saw an object bobbing on a stream near where David was last seen.
She said: "We spotted it from the bank. We were just setting up for low tide when we saw something bobbing. It was like 'quick, get the boat up, quick get the suits on'. Everything was quick," she said.
"So the boys jumped in the boat to try and catch it. It turned out to be one hell of a big stinking branch. It looked like it could be him. I had my hopes raised but dashed."
Mrs O'Halloran, who has taken a high-profile role in the search, added: "I just hoped that would be him and it would be this bloody search finished with.
"I would get some closure, some peace and get him home and sorted."
Ms O'Halloran vowed to continue the search for her son after Central Scotland Police scaled back its efforts, and is using an online fundraising site and charity single to raise money for her efforts.
Joined by David's step-father Malcolm McDougall and a local volunteer, Ms O'Halloran used the £500 dingy and two dry suits purchased with donations.
"This isn't Mother's Day to me. This is just another day to try and find David. Mother's Day doesn't exist now David is dead," she said afterwards.
The group have been meticulously combing the water from Bridge of Allan, where David was last seen on CCTV at 2.19am, out to the River Forth near Cornton Vale Prison.
The team, which usually includes a second volunteer, managed less than an hour in the dinghy looking for Ms O'Halloran's only child after a sudden blizzard forced them off the water.
Remembering last year's Mother's Day, Ms O'Halloran said: "I would probably have been given a wee box of chocolates and a card.
She described his absence yesterday as "just absolutely devastating," adding "But it's just devastating not ever having him in my life again. Not having a wee kiss and a wee cuddle and a wee 'I love you mummy'."
David was said to have played drinking games during the night out before his disappearance.
Part of his mother's active online campaigning, which has seen more than 16,000 pledge their support via Facebook, is to highlight the dangers of heavy drinking.
Yesterday she promised to continue the search for her son until he is found. "We'll keep going as long as we can. We're not giving up easy. Giving up is not in my vocabulary," she said.
Central Scotland Police said the search for David had been scaled back.
A spokesman said they were checking the area around the last sighting of the student.
He added: "The information we have from experts is that if David was suffering from hypothermia, it would be unlikely he would travel more than 2km from where he was last seen."
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