The eight-meter whale, which weighed around six tonnes (6,000 kilos or 13,200 pounds), ran aground on Saturday, prompting both locals and experts to try and save it in this coastal city some 400 kilometers (250 miles) south of Buenos Aires.
But it died on Monday, suffering from "anemia and an infectious condition," said Adrian Faiela, a vet at Aquarium, one of Argentina's main marine parks which is based in the city.
Speaking to the official Telam news agency, he said the whale had damaged fins, "which suggests a pre-existing condition before it was beached."
Efforts to rescue it began immediately with experts bringing in a crane equipped with harnesses, and on Monday they tried to tow her into the water but it didn't work.
"I was happy when it moved its tailfins but afterwards we quickly realised these were reflexive moments just before death," he said, shortly after the giant mammal died.
"It was amazing how many people came to try to help," local resident Karina Caputo told AFP.
"They did their best, both regular people and lifeguards alike, and people from the prefecture also did everything, but in the end ... "
Rodrigo Gonzálvez, head of Mar del Plata's civil defense unit, said marine experts from the city's university "would take samples from the animal" and then remove it for disposal.
