Dry Tortugas National Park Dry Tortugas National Park is a national park in the USA about 68 statute miles ( 109 km ) west of Key West in the Gulf of Mexico . The park preserves Fort Jefferson and the seven Dry Tortugas islands , the westernmost and most isolated of the Florida Keys . The archipelago ' s coral reefs are the least disturbed of the Florida Keys reefs . The park is noted for abundant sea life , tropical bird breeding grounds , colorful coral reef s and legends of shipwrecks and sunken treasures . The park ' s centerpiece is Fort Jefferson , a massive but unfinished coastal fortress . Fort Jefferson is the largest masonry structure in the Western Hemisphere , and is composed of over 16 million bricks . Dry Tortugas is unique in its combination of a largely undisturbed tropical ecosystem with significant historic artifacts . The park is accessible only by seaplane or boat and averages 60 , 000 visitors each year . Activities include snorkeling , picnicking , birdwatching , camping , scuba diving , saltwater fishing and kayaking . Geography . The Dry Tortugas are a small archipelago of coral islands located about west of Key West , Florida . They represent the westernmost extent of the Florida Keys , though several reefs and submarine banks continue westward outside the park , beyond the Tortugas . The park area is more than 99 % water . The seven major islands , all within the park , are , roughly from west to east , Loggerhead Key , Garden Key , Bush Key , Long Key , Hospital Key , Middle Key and East Key . The Park is bordered on the east , south and west by the Florida Keys National Marine Sanctuary , and on the northwest by the Tortugas Ecological Reserve . Total land area within the park is . The park is in a tropical maritime climate , with rainy seasons coinciding with hurricane season from May to October , and a drier season from November through April . The area is heavily influenced by frequent hurricanes and tropical storms . Even with exposure to tropical systems the Tortugas are among the driest places in Florida , with an annual precipitation of about . There is little temperature variation , with high temperatures in summer around and low temperatures in winter around . The northern and western portions of the park , including the central island group , were designated a " research natural area " on January 19 , 2007 , in which no marine life may be taken , nor may vessels anchor . Vessels wishing to moor in the research natural area must use designated mooring buoys or docks . About 54 percent of the park remains open for fishing . The park is west of Key West . Visiting the park by private boat is difficult because of its distance , so most visitors come by ferry or seaplane from Key West , Florida . Official ferry and transportation services to the Dry Tortugas includes the Yankee Freedom III catamaran and seaplane services . History . The first European to see the Dry Tortugas was Juan Ponce de León , who visited on June 21 , 1513 . Ponce de León caught 160 sea turtles there and subsequently referred to the islands as the " Tortugas " ( turtles ) . They are called " Dry " owing to the absence of surface fresh water on the island . The archipelago includes a high concentration of historically significant shipwrecks dating from the 17th century to the present . The Dry Tortugas were a significant American naval base from Colonial times to the early 20th century , providing a sheltered anchorage and coaling station through the Spanish - American War . Florida was acquired from Spain by the United States in 1822 . The Dry Tortugas were seen as a strategic point for the control of the Florida Straits and the Gulf of Mexico . Work on a lighthouse on Garden Key started in 1825 . Planning for a fortification began almost immediately , and construction started in 1847 . In 1856 work on a new , more powerful lighthouse on Loggerhead Key was started to replace the Garden Key light . Work was half complete in 1860 . Construction continued into the American Civil War , but eventually stopped and the fort was used as a military prison . This use continued until 1874 . With the introduction of coal - fueled ships , the Dry Tortugas became a coaling station for US Navy ships . Fort Jefferson . Fort Jefferson is a massive but unfinished coastal fortress . It is the largest masonry structure in the Western Hemisphere , and is composed of over 16 million bricks . Park history . Comprising , Fort Jefferson National Monument was designated by president Franklin D . Roosevelt under the Antiquities Act on January 4 , 1935 . The monument was expanded in 1983 and redesignated as Dry Tortugas National Park on October 26 , 1992 by an act of Congress . Dry Tortugas is presently managed by the staff of Everglades National Park . The park was established to protect the island and marine ecosystems of the Dry Tortugas , to preserve Fort Jefferson and submerged cultural resources such as shipwrecks , and to allow for public access in a regulated manner . During the Federal government shutdown of 1995 and 1996 , Dry Tortugas was closed along with all other national parks . Seeing this as having a damaging effect on their tourism - dependent economy , the residents of Key West , Florida raised money to keep Dry Tortugas open . The effort was inspired by the Smithsonian Institution , which raised private donations to keep its museums open during the shutdown . Failing to find anybody to accept the money to reopen the park , Key West residents , under the auspices of the satirical micronation Conch Republic , sent a flotilla of civilian boats and fire department boats to Fort Jefferson in order to reopen the national park . When officials attempted to enter the fort , they were cited . The citation was contested in court the following year , and the resultant case , " The United States of America v . Peter Anderson " , was quickly dropped . The park is a landing location for immigrants arriving from Cuba in homebuilt boats called " chugs . " Receiving and housing the migrants is a particular problem for Dry Tortugas , which has limited resources for such arrivals and which is several hours from the nearest Coast Guard or Border Patrol units . Communications with Key West are accomplished using a satellite - based voice - over - IP system , which is prone to garbling and delays , and by a radio relay system using an abandoned Air Force tower between Key West and the Dry Tortugas . Visitation steadily rose for several decades , reaching a peak of 83 , 704 in 2000 . Since then visitation has slowly decline , and now averages close to 60 , 000 per year . Ecology . The Dry Tortugas are classified as a borderline sub - tropical - tropical ecosystem , hosting species that do not breed or are uncommon anywhere else in the continental United States . When a cold front along Florida wiped out 96 % of branching coral in 1976 - 77 , once extensive branching coral formations became rubble fields . The Dry Tortugas National Park now consists of patch reef and branching coral rubble . Birds . Dry Tortugas National Park has an official bird list of 299 species . Of these , only eight species frequently nest within the park : Sooty Tern , Brown Noddy , Brown Pelican , Magnificent Frigatebird , Masked Booby , Roseate Tern , Bridled Tern , and Mourning Dove . The park features the only nesting colonies of Sooty Tern , Brown Noddy , Magnificent Frigatebird , and Masked Booby in the contiguous United States . Birdwatching activity peaks each spring ( usually April ) when dozens of migratory bird species can pass through the park in a single day . Many birds land inside the parade grounds of Fort Jefferson where they are often observed at close range . Common migratory warblers include the Northern Parula , American Redstart , Prairie Warbler , Hooded Warbler , Palm Warbler , Black - and - White Warbler , Common Yellowthroat , Yellow - rumped Warbler , Ovenbird , Northern Waterthrush , Black - throated Blue Warbler , Blackpoll Warbler , and Cape May Warbler , with more than 20 additional warbler species having shown up at least once . Several raptor species as well as Cattle Egret s are often seen hunting songbirds . Until early 2013 a small freshwater fountain existed beneath several seaside mahoe and buttonwood trees , and was the only freshwater source for many miles . Maintenance issues necessitated its removal , but a replacement water barrel is scheduled for installation in the fall of 2013 . Each year several bird guides offer tours of Dry Tortugas National Park during April and early May when daily bird lists can often reach 100 or more species . Exotic species . An active eradication program has resulted in the removal of " Casuarina " trees and agave from Loggerhead Key , by cutting and herbicide treatment .