GROTON, Conn. — Connecticut authorities are trying to determine the cause of a boating accident that killed two waterfowl hunters and seriously injured a third.

Officials say the hunters’ boat overturned Saturday morning off Mumford Cove near Groton. Firefighters rescued two men from the frigid water and third was found ashore after swimming to safety. Emergency responders also recovered the 16-foot motorboat.

The two men pulled from the water later died at a hospital. Their names have not been released.

A local resident called authorities shortly before 9:30 a.m. to report seeing a swamped boat with no occupants. Firefighters from Groton and U.S. Coast Guard crew responded to the scene.

The cause of the accident is under investigation by police with the state Department of Energy and Environmental Protection.