Terry Cavner and his partner had been out walking his daughter’s dog along Commissioners Quay on Blyth quayside on March 31 when they could hear a strange noise.
After stopping to listen, they could hear cries for help but could not see anyone.
Terry, 70, said: “We thought we could hear someone shouting for help but could not see anything.
"Then we saw a walking stick lying in the middle of the jetty. I went to it and had a look over the side and there was a guy in the water clinging onto one of the timber uprights.
"The river was quite rough and the water was going across his face and his whole body was shaking.
"I told my partner to call 999 and ask for the coastguard while I grabbed a life-ring and lowered it down to him and told him to put his arm through it.
"I then pulled him along to a part of the jetty with some ladders and told him to hold onto a rung and try to climb up but he was absolutely shattered.
"Within a few minutes we saw the inshore lifeboat from Blyth come, and they grabbed him, pulled him out of the water and took him back to their station.
"We will never forget the look of desperation in his eyes.”
The man, who was 73 and from Bedlington, was taken to hospital where Terry later found out he had discharged himself.
He said: “The man’s daughter contacted me to thank me, saying he was home and safe and recovering.”
Terry, who worked offshore for more than 30 years, said he was thankful he was passing at the time.
He said: “We had taken a different route with the dog, but we had also left an hour later than normal.
"I’ve never known a day like that. There was nobody out on the quayside. Normally there are fishermen about but there was none, and there was no traffic about. It was almost eerie.
"It was a really poor day. He was clinging on with just one hand at times.
"I don’t know how he survived.”