NBC 4-TV reported the dolphin got stuck by the low tide in the Gowanus Canal Friday morning. Witnesses say the animal was first spotted in the canal around 11 a.m. EST.
The dolphin was seen flapping around in the water and slamming itself up against the wall of the canal.
"It was injured on the end of its nose and on its fin on its back. There was quite a bit of blood," said one witness.
According to Riverhead Foundation for Marine Research and Preservation, which specializes in cases involving whales, dolphins, seals and sea turtles, it is very unusual for a dolphin to be that far up the canal. That usually indicates that there may be something wrong with the dolphin's health.
It is believed the dolphin likely entered the canal from the Atlantic Ocean through the Lower and Upper New York Bays and into the Gowanus Bay, which leads to the canal, about 20 miles from open ocean.
Robert DiGiovanni, senior biologist at the Riverhead Foundation, said earlier that it was unsafe to put rescuers in the polluted water and that they were planning to wait and see if the dolphin would leave on its own when the tide rose again but it was too late.
The next high tide was to occur at 7:10 p.m. EST Friday but the dolphin was reported dead by 6:30 p.m. EST.
It's unclear what responders on the scene plan to do with the dolphin's carcass.
The Gowanus Canal empties into New York Harbor and was once a major transportation route with numerous manufacturing facilities operating along its banks for years.
The U.S. Environmental Protection Agency (EPA) calls it now "one of the nation's most extensively contaminated water bodies," with pollutants including PCBs, coal, tar, waste and heavy metals.
It was added to the EPA's list of national Superfund priorities in 2010.