Three local men were trying to talk to the man – in a very distressed state – when the man fell into the river.
He was able to cling to a lifebelt until Foyle Search and Rescue volunteers arrived and were able to lift the man out of the water.
He was later taken to hospital by ambulance to be treated for suspected hypothermia.
Those who witnessed the incident told Derry Daily of how upsetting the situation was for all concerned.
And there is growing anger at the lack of in-care beds for mental health patients as staffing levels and resources are slashed.
“I saw what happened and it was just heart-breaking; this man was clearly distressed and very upset,” said one witness.
“The men on the bridge with the police and ambulance people and the foyle rescue team were all superb.
“But there is a mental health crisis in the city and no-one seems to know what can be done about it.”
Those aware of the incident say getting in-patient care is becoming increasingly difficult.
“You almost have to be at the water’s edge before you can get that care,” admitted one health official, citing cutbacks and lack of beds.
“It’s a dreadful situation in a city which has had more than its fair share of heartache.”