Police said the three men were waterfowl hunting on Mumford Cove in Groton when their boat was overturned.
All three were taken to Lawrence and Memorial Hospital.
A 16-foot open motorboat with outboard engine was recovered. The incident is being investigated by the State DEEP Environmental Conservation Police.
The three men launched out of the Bayberry Lane State Access Area in Groton.
Authorities said the men who died were residents of Connecticut, but their names are not being released at this time.
Units from the Groton Long Point Police Department, Groton Town Police, and Groton Town Fire Department assisted in the rescue.
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