The New England Aquarium says the dolphin had been in shallow water off Winthrop's Coughlin Park on Sunday.
Residents reported seeing the dolphin before midnight with a female dolphin that later died.
Aquarium officials herded the dolphin for several hours and formed a line with a sea kayak and two boats to move it a number of miles.
They used engine noise and slapped water and boats to keep it from returning to shallow water.
Aquarium officials plan to perform a necropsy on the older, female dolphin that died.
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