Crews responded along a wash near 26th and Soto streets, where the dog was balancing on a strip of concrete just above the water level. The dog walked back and forth on the ledge, ignoring a life vest and a float ring that crews threw out.
The dog was struggling against the cold currents for approximately 45 minutes, and he was clearly shaken by the sound of the nearby rescue choppers.
"This dog was a little spooked and scared. They don't' know what a helicopter is, and all of a sudden, someone swoops down on them. They're protecting themselves," said Domingo Albarran of L.A. Fire.
When rescuers were able to get close to the dog, it appeared scared and scurried away. After more than an hour, a helicopter rescue team lowered a firefighter down to retrieve the animal.
At a news conference Friday afternoon, the pilot of the helicopter Scott Bowman said St. Georges took a muzzle with him but he wasn't able to get it on, "so he decided to go for the capture."
Joe St. Georges, a 25-year Los Angeles Fire Department veteran, said he received a "real bite in the thumb" but was otherwise feeling fine.
He said he had no hard feelings toward the dog.
"I didn't really have the time to establish any rapport with the dog," St. Georges told reporters after being released from County USC Medical Center. "He's cold, he's wet, he's scared, and then here's this stranger jumping on his back for all intents and purposes, and he did what dogs do."
Emotions ran high as onlookers viewed the incident from the streets.
"I was very nervous for the dog and the guy, because the guy looked like he was having problems getting the dog out. He was tackled a little bit and he was biting him, and it was scary watching them rescue the dog," said Jessica O'Rourke, who witnessed the rescue.
It is unknown how the dog got into the river.
The dog was taken away in an ambulance to a shelter in Downey, and he's been nicknamed Vernon after the town where he was rescued.
He had no name tag and no computer chip.
The veterinarian at the Southeast Animal Control Authority says he's about 6 years old. He does not appear to be a stray, although no one has come forward to claim him yet.
He has some scrapes and his nails are worn down from trying to scramble out of that river basin. Other than that, he is doing fine.
"It's really gut-wrenching. There are no words to describe how you feel. Someone in our lien of work with compassion for animals, something like that, it's not something that you want to see," said Justin Guzman, an animal control officer.
"We're going to monitor him for any diseases he may have picked up while he was out, especially having been in the river, he could have picked up some parasites or intestinal infections and things like that," said Dr. Brad Brunskill, a veterinarian. "Especially with the storms, all kinds of nasty stuff gets washed into the river."
Vernon will be quarantined for the next 10 days or so, and he will be monitored for rabies, unless the owner shows up with proof of rabies vaccination. Then, he can be monitored at home. If the owner doesn't show up, he will be put up for adoption. The shelter has been receiving calls all through Friday with offers to adopt Vernon.
AP contributed to this report.