A 28-year-old man has died while swimming in Walden Pond.
The Middlesex district attorney says authorities responded to the body of water in Concord made famous by Henry David Thoreau at about 6:30 p.m. Sunday.
The man had been swimming with friends in an area known as Thoreau's Cove when he went under and never resurfaced. He was found about 20 yards from shore in about 12 feet of murky water after being under for about an hour.
He was pronounced dead of an "apparent drowning" at Emerson Hospital.
The man's name has not been made public and the death is not considered suspicious.
Authorities say he was swimming in a remote area of the roughly 60-acre pond far from the public beach, after lifeguards had left for the day.