The common dolphin, which had been trapped in the shallow end of Brooklyn's Coney Island Creek Thursday, was found dead Friday morning.

According to Riverhead Foundation, the body of the marine mammal, which had been swimming freely in shallow water by a bridge near Cropsey Avenue and Bay 54th Street, was found dead at 11:30 a.m., My Fox NY reports.

The dolphin was first spotted by a passerby just before 11:00 a.m., Thursday. According to the passerby, it appeared to be distressed, NY DailyNews reports. The dolphin was "swimming in circles, but also swimming up and down the canal, surfacing every 2-3 minutes," Riverhead Foundation for Marine Research and Preservation said in a Facebook Post.

Police said that it's common to see a dolphin in the ocean near Coney Island. But it is the first time the mammal to be seen in the creek, Westchester reports.

On Thursday, NYPD's Elite Emergency Services Unit and the Harbor Unit went to Coney Island Creek to remove debris to help the dolphin swim away.

After being visible for several hours, around 2:30 p.m., the dolphin appeared to try to dry itself on rocks, and then drifted slowly towards the muddy base of the creek. It had not been seen since.

"If they get in really shallow water, they can get stressed out," police Lt. Barry Duignan told CBS local. "He could be sick for having swam into such a shallow body of water like this."

Authorities said that a rising tide would have helped them with their rescue efforts. Duignan said that he had never seen a dolphin trapped in this type of water.

"I've only had this one other time," Duignan said. "It was off the ocean beach. If they get in really shallow water, they can get really stressed out."

"They tend not to come this far up - polluted waterway like this - if they're not looking for a place to die," Patricia Sener, who works nearby, told CBS local.