A worker there said he was doing "pretty good, considering ..." and knew that he'd been "a pretty lucky boy".
The motorbike, a new-looking modern machine was "not too damaged" and would be fixed by the dealership once it was delivered by the contractors who removed it from the bridge.
The truck driver, who remained at the scene and did not wish to be named, was shaken up by the accident, and initially thought he had killed the rider.
The first police officer on the scene, constable Lisa Walker said she had to stop the truckie from leaping into the water after the rider.
The truck driver said he was crossing the narrow Old Waimakariri Bridge about 7.20am today when he looked down to the choppy, flooded muddy waters below for a moment, before his right rear wheel clipped the concrete kerb and he lost control.
He was sent into a skid, broadsiding across both lanes, in front of the motorbike.
"The bike had pretty much stopped and he went over the railing," said the uninjured driver, who police say may yet face charges.
"I jumped out of the truck on the passenger's side and tried to get a rope to him.
"He was hanging on to a tree (about 30m from bridge).
"Me and some others got three straps to him but he says he couldn't hang on. He was just too cold. He had no feeling in his arms. Freezing, man.
"I'm just so glad he's OK."
The rider was suffering from hypothermia, said senior sergeant Malcolm Johnston at the scene, but otherwise was uninjured. He was saved by wearing full leathers, the officer thought.
Ms Walker of the nearby Kaiapoi police station was first on the scene after abandoning her breakfast.
She said the driver had thrown a strop but the rider was just "clinging to the tree for dear life".
After telling the rider a helicopter was on the way and to hang in there, her main job was to stop the driver from jumping into the freezing water himself.
"He was going to (jump in) ... and then we would've had two people to rescue."
A large crane removed the truck and cleared the bridge, and the damage to the guardrails was patched up by temporary barriers.
Mr Johnston said the rider was lucky the river was in flood, otherwise he would have had a 15-metre fall onto gravel.
"The man is extremely lucky to be alive," said sergeant Mike Brooklands.
"If he had lost his grip on the tree it's unlikely he would have survived in those conditions.
"The rescue personnel have done an incredible job to pull him out of the situation."
