A passerby who saved a four-year-old boy from drowning said he feared they would die in the rescue.
Mark Hopkins, 50, from Port Tennant, jumped fully clothed into the Old Prince of Wales dock, Swansea Marina, when the child plunged 6ft (1.8m) into the freezing water.
He said the terrified boy pulled him under the water three or four times, and the temperature sapped his energy.
Fortunately, an onlooker threw them a life ring and pulled them to safety.
The incident happened at around 17:00 BST on Saturday.
Mr Hopkins, a chef, said he was about to have a meal at a pub on the waterfront when he heard the boy's mother screaming.
"I could see the boy two feet under the water, I dropped my mobile phone and just dived in," said Mr Hopkins.
"I cannot watch a kid drown, you've got to do something."
But when Mr Hopkins jumped in, the water was bitterly cold.
"I have never been so cold in my life," he said. "The top two foot of water was ok but below that it was freezing.
"It was sapping all my strength.
"The boy was screaming and fighting me, he took me down three or four times, I honestly thought I was going to die."
Mr Hopkins pulled the child onto his chest and swam doggy-paddle to the dock wall.
But there was nothing to hold on to and he had to cling on to bits of brick before an onlooker threw down the life ring.
Paramedics took the boy to hospital suffering from hypothermia.
Mr Hopkins said he would visit the child after he was fully recovered.
"I don't think I'm brave - there's a child in the water and you're not going to let him die," he said.
But Mr Hopkins' daughter Jody added: "He says that he isn't a hero and that it was just instinct.
"But I think he is amazing, he's a real hero."
Steve Matthews, of Swansea Coastguard, said it appeared the child's mother had been feeding her other child, aged one, and lost sight of her son who ended up in the water.
"The advice we have for those around the marina is to make sure that you have got a visual of your children and watch them as best you can around any water source," he said.
"If they're a toddler take precautions, for example putting them in reins."