The comes after one of them was found dead in the Navesink River on Wednesday.
Bob Schoelkopf, co-director of the Marine Mammal Stranding Center, said it died from pneumonia. And he says it's the same dolphin that had been observed coughing a few weeks ago.
Schoelkopf told the National Oceanic and Atmospheric Administration about the dolphin's condition.
But officials there, who have jurisdiction over the dolphins, have resisted calls to either scare them out of the rivers or physically remove them by netting them.
However, the dolphin's death has some elected officials in New Jersey calling on the NOAA to intervene sooner rather than later.