By Jonathan Allen

NEW YORK (Reuters) - A dolphin that died in a polluted New York canal last week was old and sick, and the toxic waters where it spent its final hours played little, if any, role in its demise, a biologist who examined the dolphin's carcass said on Tuesday.

The male common dolphin had not eaten in some time even before swimming a mile inland up Brooklyn's Gowanus Canal, where it was discovered on Friday morning, said Kimberly Durham, the biologist who performed the necropsy.

The dolphin died later on Friday. Its death, news of which spread quickly, prompted some observers to argue that more could have been done to save it.

"Whether it was in the Gowanus Canal or on a sandy beach on Jones Beach, this animal's fate was not promising," said Durham, the rescue program director at the Riverhead Foundation for Marine Research and Preservation. "This animal was compromised and had chronic ailments."

Even at 340 pounds (154 kg), the seven-foot-long (2.13-meter) dolphin was noticeably thin, Durham said. It had stomach ulcers and kidney stones as well as worms and other parasites, she said.

Wear on its teeth suggested it was about 25 to 30 years old, toward the high end of the species' natural lifespan, she said.

Durham said while many people have a fondness for dolphins, they might overestimate the degree to which those feelings are returned.

"This animal wasn't coming into the canal to seek humans' help," she said. "I think it's always interesting that people believe that dolphins think humans are the most amazing things out there. We're not even on their radar."

The death might have gone unnoticed had the aging dolphin not spent its final hours in such bleak surroundings within easy reach of New York City's high concentration of journalists and television crews, bloggers and social-media enthusiasts.

Its death was intensely discussed and scrutinized online over the weekend.

The dolphin had no skin lesions nor fluid in its respiratory tract that might be expected if the waters of the notoriously polluted canal played a major role in its death, she said.

Common dolphins are social creatures, and it is unusual for an animal to separate itself from its pod unless it is sick or dying, Riverhead biologists had said.

Durham said police had warned it was too dangerous to go into the canal, which has been declared one of the most polluted U.S. water bodies by the Environmental Protection Agency.

Even if biologists had made the risky approach, it was not clear that would have achieved much other than to add to the animal's distress, Riverhead officials said earlier.

(Editing by Ellen Wulfhorst and Dale Hudson)