No one has been charged and foul play is not alleged in an incident that left one man dead and sent another to the hospital last night after rescue efforts by four separate public safety agencies, Suffolk County District Attorney Daniel F. Conley said.

Massachusetts State Police, fire departments from Boston and Cambridge, and Boston Emergency Medical Services personnel responded to the area of the Harvard Bridge, which traverses the Charles River along Massachusetts Avenue, at about 11:00 last night for a report of two men in the water.

An ongoing death investigation by State Police detectives assigned to Conley’s office indicates that one man, a 28-year-old Hyde Park resident, jumped into the water from the bridge and that a friend, a 27-year-old Dorchester man, followed suit in an effort to rescue him.

Responding State troopers threw their cruiser’s spare tire into the river for use as an improvised flotation device. After several attempts, the 27-year-old man was able to grasp it and was subsequently brought to shore after about 20 minutes. That man was brought to Brigham and Women’s Hospital for evaluation and is expected to survive.

About an hour later, the body of the 28-year-old man was recovered by members of the State Police Marine Section and Cambridge Fire Department. Emergency medical technicians pronounced him dead at a nearby boat landing shortly before 1:00 this morning. An autopsy is expected to reveal the cause of his death today.

Because neither man is accused of a crime or believed to be the victim of a crime at this time, their names are not being released.

State Police detectives assigned to Conley’s office investigate all homicides and unattended deaths on state highways, waterways, and property within the City of Boston.