The 8 to 15 mammals were first spotted in the Hackensack River on Wednesday. They've been swimming near Hackensack, Teaneck and Bogota.
Bill Sheehan of the Hackensack Riverkeeper group fears there's not enough food in the river in the winter to sustain the dolphins.
The Marine Mammal Stranding Center in Brigantine has been contacted. The center says it can't act until the dolphins are in distress.
