Experts are analyzing water temperature and oxygen levels and other factors to try to explain the massive die-off about 300 miles south of Santiago, the BBC reported Thursday.
"We're investigating the Coronel Bay to establish the physical parameters of temperature, electric conductivity and, above all, the oxygen," local environment official Victor Casanova said.
Local fishermen said they believed the deaths might have been caused by local power stations that use seawater for cooling.
"I'm 69 years old and started fishing when I was nine, but as a fisherman, I never saw a disaster of this magnitude," Gregorio Ortega told a local radio station.
Concerns about the impact on the livelihood of the local fishing community were expressed.
"The way everything is being destroyed here, come the high season in November, we're already thinking we won't have anything to take from the sea," Marisol Ortega, a spokeswoman for the fishermen, said.