A dolphin was discovered dead in the Hudson River Thursday, June 21, 2012. View Full Caption DNAinfo/Mathew Katz

CHELSEA — A dead dolphin was found floating near Chelsea Piers Thursday morning, days after one was spotted swimming on the Hudson River, officials said.

A spokeswoman for the Riverhead Foundation, which had been searching for the lone dolphin since it was seen in the Hudson Sunday evening, said it was too soon to say whether the dead dolphin was the same as the one that was spotted Sunday.

"We won't know if it's the same dolphin until we match the dorsal fin," said Kim Durham, spokeswoman for the foundation, which monitors marine mammals in New York.

But sources said that it was highly likely, given the rarity of lone dolphins in the Hudson River.

The common dolphin's carcass was found near Pier 59 in Chelsea, and was secured by Chelsea Piers staff until a crew from the Riverhead Foundation could arrive to inspect it, Durham said.

She said it was too early to determine the cause of death.

Scott Seisler, general manager of the marina at Chelsea Piers, said he made the grim discovery about 7 a.m. Thursday.

"We called the Coast Guard and tried to figure out what to do with it," he said, adding that the dolphin was found hitting up against the docks.

"It’s sad, the poor little animal. I feel bad for the dolphin."

A crew from Riverhead Foundation arrived Thursday afternoon to retrieve the dolphin and bring it back to their Long Island facility to determine the cause of death.

James Sullivan, a marine mammal stranding technician for Riverhead, didn't immediately notice any injuries on the dolphin's body.

"There was no obvious unusual trauma," he explained of the 150-pound dolphin, noting that it had been dead in the water about four hours. "In some cases it will be emaciated by being outside, but he’s been floating all morning. We don’t know if he’s bloated from saltwater."

Sullivan added that it's not rare to find dead dolphins in the city's waterways because of their attraction to the waters here.

"They come here because the water heats up and their food sources bloom — things like mackerel, herring and other small bait fish," he said.

Sullivan added that his organization receives about 15 to 20 calls a year, mostly regarding live seals.

An autopsy on the dolphin will be done either Friday or over the weekend, Durham said.

She encouraged anyone who sees a marine mammal in distress in the future to call the foundation's hotline at (631) 369-9829.