BOSTON (WHDH) -- A large dead, floating Finback Whale in Boston Harbor provided a shocking and rare sight Sunday.

Researchers said the whale may have come from a marine sanctuary 25 miles east of Boston, a spot where whale watchers commonly see the endangered Finback species.

“It’s probably likely that this animal probably died outside of the harbor due to natural causes or maybe due to something related to a gear entanglement,” said Tony Lacasse of the New England Aquarium.

Coast guard boats have been keeping an eye on it to ensure boats don’t collide with the carcass. The plan so far, is to let the whale float.

“We’re in an area that’s got two and a half million people in a short distance from there and we’re talking about an animal that has got probably 80 to 90 thousand pounds of rotting flesh so we’d have to be very deliberate, you know, in terms of where we would bring that kind of animal ashore,” said Lacasse.

Researchers said the 50 to 60-foot-long male whale was probably 10 to 12 years old. But if the whale doesn’t wash ashore somewhere there will be no way to figure out how he died.

“Several years ago we had a dead whale right at the mouth of the harbor and also about the same time one spring day we actually had a young humpback whale swim all the way in to behind the aquarium near Quincy market,” said Lacasse.

Researchers said if the whale naturally washes up closer to land they will try to pull it ashore and dissect it to determine the cause of death. As for how the whale got into the harbor, they said it is possible it just floated in or a boat hit the body, pushing it close to the harbor.