After days of rescue efforts, the dolphin discovered in the South River died Saturday.
The Marine Mammal Stranding Center says the dolphin died after rescue teams tried to guide him toward the Raritan Bay.
The animal was first spotted in the river Wednesday near the Old Bridge-East Brunswick border.
When officials saw the dolphin Saturday he was having a seizure and struggling to breathe.
Authorities say the emaciated animal had no energy left to swim and had gone up the river to die.