Roger Ryder said it was a miracle his son spotted the car in the river.
"I couldn't believe my eyes. It took me a while to see it myself and when I did I ran down the bank but ended up falling all the way down and landed on some rocks. I'm a bit sore now, but all I could think was getting to the guy.
"I felt his neck for a pulse and I couldn't find one so I panicked and ran back up the road and jumped back into my car and floored it to the nearest driveway to get an ambulance," he said.
He went back down and the emergency services were there and the man was talking to his rescuers.
"I told him. 'Man, you were gone, you weren't breathing,' and he didn't believe me. He was only a young fella. I hope he learns his lesson after this," he said.
"That's a bad corner. It is the second accident we have come across on the same stretch of road. They really need to install crash barriers there," he said.
The man was listed as being in a stable condition last night.