UPDATE: The dog is in stable, but serious condition.
The person taken into custody is described as a juvenile, officials say.
Authorities are investigating why a dog fell from the Phil Foster bridge on Wednesday.
Witnesses claim a woman threw the dog from the bridge.
It happened around 4 p.m. at Phil Foster Park. A lifeguard on the scene says the dog fell 30 feet and landed on sand and rocks below the bridge, several yards from the swimming area.
The dog, which is a black and white 8 year old Jack Russell terrier, tried moving after he landed but collapsed. PBC Animal Care and Control said the dog has a broken back.
ACC could not confirm if the dog was thrown but says the dog belonged to a juvenile who was on the bridge. It is unknown if the dog belonged to the woman or someone else.
A lifeguard consoled the dog while they waited for ACC to arrive. The dog was transported to the ACC facility for treatment. His condition is unknown.
Witnesses say the woman who claimed to have thrown the dog seemed appeared to be mentally unstable.
"She was on foot and came down off the bridge. She had taken her pants off in the parking lot, removed her clothing. And went in the water and the police eventually took her away," said Laura Weinberger, who was snorkeling nearby when it happened.
Witness Jordan Harrison said it was disturbing to see the dog in pain.
"She walked over to the beach and into the water casually, didn't seem to show any concern for the dog at all," he said.
"It was beautiful to see the lifeguard petting and consoling him. People said they wanted to adopt him, so I hope he makes it okay," said Weinberger.
The woman, whose identity is unknown, was taken into custody.
The Palm Beach County sheriff's office is leading the investigation into what happened.