Dry Tortugas National Park

Dry Tortugas National Park sits 70 miles west of Key West in the Gulf of Mexico, a cluster of seven low coral islands surrounded by 64,701 acres of open water — more than 99 percent of the park is sea. Accessible only by a 2.5-hour ferry ride or a 40-minute seaplane flight, it is among the most remote national parks in the eastern United States and one of the least visited, drawing about 81,000 people in 2023 to rank 61st among all 63 national parks. The park's dominant structure is Fort Jefferson, a six-sided brick fortification begun in 1846 that covers most of Garden Key and is the largest masonry structure in the Americas — built from approximately 16 million bricks over 30 years yet never fully completed and never fired in battle. The surrounding waters hold sections of the Florida Reef, some of the clearest water on the East Coast, and a suite of wildlife that includes nesting sea turtles, one of the largest sooty tern colonies in the United States, and abundant reef fish visible from the surface without scuba equipment.

Fort Jefferson, the six-sided Civil War-era brick fortification on Garden Key that covers nearly the entire island — one of the largest masonry structures in the Americas, built from roughly 16 million bricks, and still largely intact more than 150 years after construction began.
Snorkeling and diving in water clear enough to see the bottom at 25 feet from the surface, with coral formations along the fort's moat wall and the Windjammer Wreck — a 19th-century iron sailing ship resting in shallow water off Loggerhead Key.
The sooty tern colony on Bush Key, where approximately 80,000 to 100,000 terns nest each year from January through September in one of the largest seabird colonies in the United States, visible and audible from Garden Key.
Sea turtle nesting from May through October, when loggerhead, green, and hawksbill turtles haul onto the beaches and the surrounding water is a regular feeding and resting habitat for sea turtles year-round.

By ferry: The Yankee Freedom III is the standard access for most visitors. The vessel departs from the Key West Historic Seaport at 8 a.m. and reaches Garden Key in approximately 2.5 hours, with a 4-hour stay before the 2:45 p.m. departure. Book tickets well in advance through the Yankee Freedom website; the boat has a fixed capacity and spring dates sell out far ahead. Campers can check extra gear for an additional fee.

By seaplane: Key West Seaplane Adventures operates half-day and full-day flights from Key West Airport. The flight takes about 40 minutes each way and offers an aerial view of the fort and surrounding reef before landing on the water near Garden Key. Half-day trips allow roughly 2.5 hours on the island; full-day trips allow about 4 hours. Seaplanes carry a small number of passengers per flight; book early.

By private boat: The park is accessible to private vessels, with designated mooring buoys around Garden Key and a dock for day use. Anchoring near the moat wall and snorkeling from the boat is a common approach for boaters out of Key West or the Florida Keys. The NPS charges a mooring fee; check the park website for current rates and regulations.

By air to Key West: Key West International Airport (EYW) is the jumping-off point for both the ferry and the seaplane. EYW is served by several major carriers with connections through Miami, Atlanta, and Charlotte. The airport is small and demand exceeds supply in peak season — fares can be high. Miami International (MIA), about 160 miles north, offers more flight options and lower fares with a 3-hour drive to Key West.

The Dry Tortugas are low coral reef islands — essentially sand, shell, and organic debris accumulated on top of the Florida Platform, the same broad carbonate limestone shelf that underlies the entire Florida Keys and southern Florida. The islands rise only 3 to 6 feet above sea level at their highest points, a consequence of their purely depositional origin. There is no bedrock, no soil in the traditional sense, and no elevation from which fresh water can accumulate and drain — which is why Spanish mariners labeled them "dry" on navigation charts as early as the 16th century.

The Florida Platform on which the keys sit is a massive carbonate shelf built up over tens of millions of years from the skeletal material of corals, mollusks, and other marine organisms. The Dry Tortugas mark the southwestern tip of this shelf, where the platform edge drops steeply into deep Gulf of Mexico water. The surrounding reef system is part of the Florida Reef, the third-largest barrier reef tract in the world and the only living coral barrier reef in the continental United States, stretching about 360 miles along the Florida Keys.

Fort Jefferson's construction exposed an unusual geological challenge: the islands provided no local building material whatsoever. All 16 million bricks, plus sand, lime, and hardware, had to be shipped from the mainland. The weight of the completed fort caused measurable subsidence of the island beneath it; some sections of the lower walls are now below the high-tide mark and experience regular flooding, which has accelerated the deterioration of the mortar and brick. The fort was never finished partly because engineers discovered midway through construction that the foundation could not support the full three-gun tier design without sinking further.

Coral reef growth around the islands occurs actively where water quality and temperature allow. Water temperatures in the 78–82 °F range in summer and 68–74 °F in winter remain within the tolerance range for reef corals. The reef supports more than 300 species of fish, 31 species of coral, and a variety of invertebrates, with the clearest water and richest reef development typically occurring on the western and southern sides of the island group, away from the sediment influence of Florida Bay to the north.

The sooty tern colony on Bush Key is one of the defining wildlife events in the eastern United States. Approximately 80,000 to 100,000 sooty terns pack the small key each year from late January through September, nesting shoulder to shoulder in one of the largest breeding colonies of the species in North America. Brown noddies nest alongside the terns. Magnificent frigatebirds — large, fork-tailed seabirds with a 7-foot wingspan — roost and nest on bush key as well, and their territorial harassment of other birds returning with food is a constant spectacle from the fort's upper walls. Bush Key is closed to visitors during nesting season to avoid disturbance.

Sea turtles are present year-round. Loggerhead turtles are the most common; they nest on Garden Key and neighboring beaches from May through October, and green and hawksbill turtles also use the park's beaches less frequently. Turtles are regularly seen from the moat wall and the ferry approach to the island, resting at the surface or feeding in shallow water. The park waters are a designated critical habitat for sea turtles.

The reef and moat waters support more than 300 fish species visible while snorkeling or from the moat wall. Parrotfish, French angelfish, blue tang, sergeant major, barracuda, and large nurse sharks — docile bottom-dwelling sharks that rest on the sand in the moat — are common sightings. Spotted eagle rays are seen in open water. The moat also shelters sea urchins, queen conch (a protected species), and a variety of coral and sponge species.

The Dry Tortugas lie directly in the path of the Atlantic flyway and serve as a critical landfall for migratory birds that have flown overnight across open water from the Yucatan Peninsula or Cuba. In April and May, and again in October, exhausted migrants land on Garden Key in remarkable numbers: dozens of warbler species, vireos, tanagers, and orioles that have no energy to continue. Serious birders time visits around these windows. The park's bird list exceeds 300 species despite the tiny land area.

The islands were first documented by Europeans on April 2, 1513, when Juan Ponce de León's fleet encountered them while searching the Gulf of Mexico. Ponce de León's pilot recorded the islands as "Las Tortugas" — the turtles — because the crew caught 160 sea turtles in the waters around them in a single night, enough to feed the fleet for weeks. Subsequent navigators added "Dry" to the name on charts to warn that the islands had no fresh water — a critical distinction in an era when running out of water at sea was fatal. The islands became a navigational waypoint and a victualling stop for ships moving between the Atlantic and the Gulf.

The United States recognized the strategic importance of the islands after the War of 1812. A fort at this position could control the Straits of Florida and the approach to the Gulf of Mexico — key shipping lanes for cotton and goods moving between southern ports and the Atlantic world. Congress authorized construction of Fort Jefferson in 1845, and work began in 1846 under Army engineer Captain Daniel Woodbury. The fort was designed to mount 450 cannons across three tiers and hold a garrison of 1,500 soldiers, covering every approach to the anchorage. Construction continued for nearly 30 years and consumed approximately 16 million bricks, most of them manufactured in Maine and Virginia and transported by sea. The fort was never completed: engineers eventually determined that the island's foundation could not support the full weight of the intended third gun tier, and changing military technology — rifled artillery that could penetrate masonry walls — made the design obsolete before it was finished.

During the Civil War, the Union garrison at Fort Jefferson kept the fort out of Confederate hands and used it as a military prison for deserters and those convicted of war-related crimes. Its most famous prisoner was Dr. Samuel Mudd, a Maryland physician convicted of conspiracy in the assassination of President Abraham Lincoln for setting the broken leg of assassin John Wilkes Booth the night after the April 14, 1865 shooting. Mudd and three other convicted conspirators were held at Fort Jefferson. In 1867, yellow fever swept through the garrison; Mudd, who had some medical training, treated the sick and was credited by many survivors with limiting the death toll. President Andrew Johnson pardoned Mudd in 1869.

The Army abandoned the fort in 1874 after yellow fever outbreaks made it untenable as a garrison. It served briefly as a coaling station and a quarantine facility before being largely left to its own devices. President Franklin D. Roosevelt established Fort Jefferson National Monument on January 4, 1935, protecting the fort and surrounding waters under NPS management. Congress redesignated the area as Dry Tortugas National Park on October 26, 1992, adding the title of national park and strengthening environmental protections for the surrounding reef.