Daniel Scott was recovered unconscious from the water after a multi-agency search for him in November last year.
Now he has teamed-up with the rescue services that saved him to warn others about the dangers he faced.
Mr Scott’s ordeal began when he became separated from friends after a night out in Lewes.
He neded to answer a call of naturewhen near the River Ouse south of the town at 3am. He jumped over a fence - but soon found himself submerged in water in pitch blackness.
He said: “I took a step and I felt my foot get wet, then my thighs.
“While trying to work my way out, I realised I was up to my neck. My face was then covered and I had no idea where the riverbank was.
“I thought ‘I’m in a really bad situation now’.”
But a man heard his distress and dialled 999. It sparked a painstaking search of a three-mile stretch of the river.
Mr Scott was found alive, a mile and a half from the nearest road, after a police helicopter located a faint heat source.
He had been in the water for more than 90 minutes and his body’s centigrade temperature had plunged to the mid-twenties - hypothermia occurs when the body temperature goes below 35C.
“I probably should have been dead,” added Mr Scott, from Uckfield.
Paul Coppard, station manager at East Sussex Fire and Rescue Service, said: “It started with Mr Scott taking one step too many and entering the water. It was the early hours of the morning and freezing cold and it’s a tidal river.
“Daniel was swept some considerable distance from where he entered the water so I consider him incredibly lucky to have survived.”
Mr Scott’s story has been told on a video issued by East Sussex Fire and Rescue Service in the hope of reducing accidental drownings in the UK.
Dawn Whittaker, National Fire Chiefs Council lead for drowning prevention and water safety, said: “If it happens to you, shout and make yourself heard. Try not to panic and just think ‘float to live’.”
Float to Live is the slogan for the Respect the Water campaign. The advice is while you float, you can regain control of your breathing and your heart rate can begin to steady. If you find yourself in the water, relax and float for up to 90 seconds – the time it takes for cold water shock to disappear.