David Waggitt, 25, rushed into the River Eden to grab the young man and pull him to the banks after he and his horse got into difficulty. The teen was rushed unconscious to hospital but it is believed he has since made a full recovery.
David was at Apple Horse Fair in Cumbria with his partner Chantelle and their eight-year-old and six-year-old sons when the drama unfolded.
The horse broke free from its rider in the river and so David, a scaffolder, dashed to help.
Speaking to Chronicle Live, the dad said: “I was about 40 metres away down the bank and no-one was doing anything to help. It was when I saw his feet sticking in the air I decided to do something.
“I ran down the bank and swam towards him. I couldn’t see him at first so just reached under the water and managed to grab him and pull him to the surface and to the bank. The crowd started clapping when I got him out.
“It was all pretty scary but I’m glad the lad and the horse seem to be OK.”
The father, from Gateshead, Tyne and Wear, added: “He was unconscious and his lips were blue. We were really worried for him. The ambulance came and took him away.
“Fortunately he’s alright now. He came back the next day to find me and thank me. Apparently the horse is recovering with the RSPCA.”
Video shared online shows spectators scream in horror as the teenager struggles in the water.
David and other men are seen rush in to save the lad.