KEY WEST, Fla. (WFLA) — Archaeologists have found the remains of a 19th-century quarantine hospital on what was once an above-sea island in the Florida Keys, according to the National Park Service.

Monday, Dry Tortugas National Park announced the discovery of the archaeological site near Garden Key. It was found as part of a survey first conducted in August 2022 by cultural resources staff, the National Park Service’s Submerged Resources Center, the Southeast Archeological Center, and a University of Miami graduate student.

Park officials said the hospital was used to treat yellow fever patients from Fort Jefferson between 1890 and 1900.

So far, only one grave has been identified. Officials said it belonged to laborer John Greer, who died on Nov. 5, 1861, of unknown causes while working at Fort Jefferson.

According to the National Park Service, Greer’s grave was a headstone-shaped slab of greywacke, which was the same material used in the construction of Fort Jefferson’s first floor. It bore his name and date of death.

Historical records suggest that the Fort Jefferson Post Cemetery once held the graves of dozens of people, most of them being U.S. soldiers.

“This intriguing find highlights the potential for untold stories in Dry Tortugas National Park, both above and below the water,” Josh Marano, maritime archeologist for the south Florida national parks and project director for the survey, said in the news release. “Although much of the history of Fort Jefferson focuses on the fortification itself and some of its infamous prisoners, we are actively working to tell the stories of the enslaved people, women, children and civilian laborers.”

Officials said aside from its history as a prison during the American Civil War, Fort Jefferson also served as “a naval coaling outpost, lighthouse station, naval hospital, quarantine facility,” harbor, and military training center.

As the population of the fort increased, the risk of diseases like yellow fever also rose, leading to outbreaks that killed dozens of people in the 1860s and 1870s.

The National Park Service said this required some of the islands surrounding Garden Key to be fitted with quarantine hospitals. Many of the hospitals closed after Fort Jefferson was abandoned in 1973, but when the U.S. Marine Hospital Service took charge of Fort Jefferson in 1890, this required another isolation hospital to be developed on a nearby key.

Officials said the hospital’s underwater location showed the impact of climate change and storm events on the Florida Keys. Archaeologists are still working to learn more about Greer and the others interred at the Fort Jefferson Post Cemetery.