The seal, which onlookers said was playfully swimming around and eating fish in Grangebel Park, did not appear to be in danger, according to biologists with the Riverhead Foundation for Marine Research and Preservation.
Kim Durham, the rescue coordinator for the Riverhead Foundation said the animal looked small for a harbor seal, indicating that it was most likely a pup.
The seal was feeding on alewives near a recently installed fish ramp, which helps the fish migrate up the river to spawn.
“If there is an area that has food, they will come in,” Ms. Durham said of seal behavior.
The seal was first spotted about 10 a.m. Tuesday morning by construction workers in the park, just west of Peconic Avenue in downtown Riverhead.
One of the workers, Mike Jones, said it appeared to be in good spirits.
The seal was even putting on a show while people were taking its photo Wednesday afternoon, he said.
“He was eating fish and spinning around in circles,” Mr. Jones said. “He was having fun.”
Ms. Durham said another harbor seal was spotted in the same area about a month ago, though closer to the Peconic Bay. She could not say whether or not it was the same animal.