Two people who live nearby reportedly spotted the killer whales, or orcas, in the beach town of Mar Chiquita early Monday and called authorities.
About 150 people, which mostly included volunteers from the area as well as city workers, firefighters and marine biologists, came to help and managed to pull six orcas to safety in the six-hour rescue operation, La Nación reported.
A vessel reportedly accompanied the whales to prevent them from turning back to shore.
Most of the volunteers reportedly had no experience with this kind of rescue operation, which included ropes used to drag the whales weighing between three and four tons back into the water.
“I regret that we could not move the biggest one, he died there in front of us,” volunteer rescuer Natalia Villa, 20, said.
“I never thought about the cold or the effort, I just wanted to return them to the sea,” rescuer Andrés Ersinger told La Nación.
At least two rescuers reportedly had to stop rescuing the whales and needed to be treated for hypothermia.
Officials said it was unclear why the orcas had beached themselves.
Flavia Lagune, Mar Chiquita’s tourism secretary, told La Nación it was possible the whales had lost their orientation because they showed no sign of illness.
Investigators planned to perform a necropsy on the orca that died.
The Associated Press contributed to this report.