Authorities in Brazil said an attempt to kill a beached right whale using lethal drugs was unsuccessful.
Scientists were trying to end the whale's suffering because it is too weak to survive back at sea.
Biologist Karina Groch told the Terra website that veterinarians were considering whether to try different drugs.
The 40-ton, 50-foot animal became stranded on Tuesday at the Praia do Sol beach.
Biologists and volunteers were splashing water on the whale to try to make it more comfortable.