Reece Taylor, 27, was out cycling alongside Norwich Yacht Station in River Wensumh, when he heard a bloke shouting for help to save his dog.
Prior to Reece arriving on the scene, Bentley, an Italian cane corso, had fallen off the side of a boat moored on the river.
Quick-thinking Reece whipped off his clobber and jumped into the river to rescue Bentley, but the distressed dog ended up biting his face in the process.
Reece explained: "I was cycling along the road and saw a woman's partner in the middle of the road amidst cars and early morning runners.
"I could hear the man saying, 'Please help, my dog is going to drown'.
"When I was growing up my mum was like the local animal shelter - we had dogs, cats, rabbits, a pet pigeon called Swark, turkeys: any animal we had it.
"I knew I couldn't cycle past and not help.
"So I just stopped my bike, stripped down into my undies on the side of the road - didn't even hesitate and jumped straight in."
Deliveroo driver Reece was able to get the 60kg dog to safety but was bitten just above his left eye as he did so.
Bentley is owned by Jade Lanigan and Jacob Williams who were on a boating holiday in the city with their son Jamie.
Jacob had attempted to rescue the dog before Reece turned up but wasn’t able to due to Bentley’s weight.
With the help of Jade's pulling, Reece managed to get a rope around Bentley, and pushed the dog onto the boat, with one hand on the boat and another around the dog's back.
Reece went straight to the walk-in centre and was told to head to the Norfolk and Norwich University Hospital where a surgeon put stitches in his right eyebrow.
Despite the injury, Reece has absolutely no regrets about jumping in to save Bentley.
Reece said: "If I had cycled past and saw the dog drown in the river I would never have been able to live with myself knowing I could have helped.
"I didn't even notice the injury whilst I was in the water - it must have been the adrenaline - but he was so scared.
"I'm so happy to have helped the family and their beautiful dog."
Jade said: "Reece was just so happy to see the look on our traumatised faces that we had our very heavy dog back.
"We want to thank the brave young man with all our hearts."Featured Image Credit: SWNS