A student at Harvard Summer School apparently drowned in the Charles River after "going into the water off a footbridge," authorities and university officials say.

Massachusetts State Police didn't specify in a news release if the man jumped or fell, but Middlesex County District Attorney Marian Ryan said investigators believe the drowning was accidental.

Ryan identified the man as 18-year-old Tyler Greene, of Georgia. WAGA-TV in Atlanta reported that Greene was from Dallas, Georgia. The prosecutor released no further details.

Witnesses reported seeing the man go into the river off the Weeks bridge in Cambridge around 8:45 p.m. Friday, come up with his arms flailing, go under again and not come back up, state police said. He was found about 25 minutes later by Cambridge Fire Department divers and taken to a hospital, where he was pronounced dead.

Sandra Naddaff, dean of Harvard Summer School, sent an email to summer school students announcing Greene's death, according to The Harvard Crimson student newspaper.

"It is with deep sadness that I share that one of our students, Tyler Greene, tragically passed away yesterday evening," Naddaff said in the Saturday morning email.

A gathering in Greene's honor was held Saturday in the Eliot House Junior Common Room at the university, with counselors and clergy members present for support, according to The Boston Globe.

Harvard Summer School is the oldest academic summer program in the United States, according to the program's website.