The marine mammal died Friday evening in the Gowanus (guh-WAH'-nuhs) Canal that runs through Brooklyn.
Experts from the Riverhead Foundation for Marine Research and Preservation were conducting a necropsy Sunday afternoon to determine the cause of death.
Results were not expected immediately.
The dolphin had riveted onlookers as it splashed around in the filthy water and shook black gunk from its snout.
The dolphin likely entered the canal from the Atlantic Ocean and got pinned at low tide.