Sonny Ferry, 19, died after a night out in York in April 2019.
An inquest in the city today heard that Mr Ferry had been on his first visit to York for a job as a labourer and had gone into the city centre with colleagues Luke Lockwood and Ben Alder on April 12.
The group went to Kuda nightclub, and Mr Ferry was seen in CCTV footage walking in the wrong direction to his hotel in Bootham after being removed from the club.
Mr Lockwood wept as he gave evidence in the inquest, telling assistant coroner Jonathan Leach that they had felt like they were "on a lads' holiday".
Alarm bells were sounded by Mr Lockwood when Mr Ferry didn’t turn up for work the next day, and his body was recovered from the Foss near Blue Bridge Lane on April 14.
The inquest heard that Rana Alzahany, who lives near Blue Bridge, heard a splash and a voice crying out for help at around 4.30am the morning Mr Ferry was last seen.
She called 999, and police and fire rescue services searched the area for an hour. They then resumed the search the next day.
It was later discovered that Mr Ferry’s debit card had been used after his death. Police arrested a 45-year-old on suspicion of theft of the wallet, who was later released without charge.
An internal police investigation found no evidence of police wrong-doing, but Mr Ferry’s mother Kate, from Ketton, Rutland, said the family had not ruled out a third party being involved in their son’s death and believed it hadn’t been investigated adequately.
But assistant coroner Jonathan Leach recorded a verdict of accidental death after hearing from police that there was no evidence to suggest foul play.
Mrs Ferry, 49, said: “I do understand how difficult it is for police officers to get it right. I’m not convinced that there wasn’t a third party involved.
“I don’t want to believe it was anything other than an accident but I had a duty to look into it.”
Speaking after the inquest, Mrs Ferry, who has three other children with her husband Steve, said: "I am unconvinced. I'm not sure the coroner took into account the information I've given him.
"It feels a bit like it was going to be a foregone conclusion. The last thing I'd want is for my son's death to be anything other than an accident but I don't believe the evidence could be described as being non-suspicious.
"I think there should have been door-to-door enquiries to see if anyone else had heard anything.
"I think they were too soon to just think 'he's been out drinking and he's fallen in the river, that's what happens in York'"
Paying tribute to her son, she said: "Sonny was a dream, hilarious, lovely, a bit of a nightmare with money, fearless, naive. He had never been to a big city like York before.
"I know he would have been frightened.
"He was a darling. I did my best as a mother to raise him as a happy boy. He was so sweet and a lovely friend.
"His name was Sonny but he was called Sunshine by a lot of people because that's what he was. He'll always be here because the sun's always here."
Mrs Ferry said the family have struggled with not knowing if Sonny tried to ring them before he died, as the phone lines were down in their area on the night he died.
They have channelled their grief into fundraising for a new lifeboat for York, and raised over £32,000 towards the £45,000 costs.
Mrs Ferry said: "I chose to grieve through positivity. It's been such a wonderful thing to do, it's been like therapy."
Speaking after the inquests, David Wilson, incident manager at York Rescue Boat, said he was concerned river accidents will rise as lockdown restrictions lift. He said: “We’ve had restrictions for a year, and we’re going to see an influx of people coming to York because of the nice weather, and that’s a concern.
“The majority of jobs we go to are mental health related, and there’s a concern that the stress and pressure of this year will be weighing on people.”
Mr Wilson said the boat's team of volunteers will resume proactive trips starting next week to keep an eye out for people in danger near the river, and that they are working on an education campaign with the two universities to improve safety knowledge.
To donate to the lifeboat in memory of Sonny Ferry, visit https://www.gofundme.com/f/the-sunshine-campaign.