A north Fulton County man drowned Thursday while snorkeling with others off the Florida coast, according to police.

John Marshall, 71, of Johns Creek, was in the water and returning to a 25-foot private vessel shortly after noon when he was spotted face down in the water, the Monroe County Sheriff’s Office said. Marshall was with nine others near Carysfort Lighthouse off the coast of Key Largo, the sheriff’s office said.

Others pulled Marshall back to the boat and a second boat, with a doctor aboard, pulled up beside it, deputies said. The doctor administered CPR on Marshall, but he was pronounced dead after being brought to shore by members of the Fish and Wildlife Conservation Commission.

An autopsy is being performed to determined Marshall’s cause of death.