Question: Off which coast of Florida is Boot Key Harbor?

Context paragraphs:
Boot Key Harbor: Boot Key Harbor is a natural body of water located in the middle of the Florida Keys, entirely within the city limits of Marathon, Florida, United States.

Marathon, Florida: Marathon is a city on Knight's Key, Boot Key, Key Vaca, Fat Deer Key, Long Point Key, Crawl Key and Grassy Key islands in the middle of the Florida Keys, in Monroe County, Florida, United States.  As of the 2000 census, the city had a total population of 10,255.  As of 2014, the population estimated by the U.S. Census Bureau was 8,708.

No Name Harbor (Key Biscayne): No Name Harbor is a natural harbor on Key Biscayne, Florida.  It is located within the boundaries of Bill Baggs Cape Florida State Park.  In the 19th century, the site served as a food-rich rookery for herons, egrets, and other species of wildlife.  Originally, the site was privately owned prior to the creation of the state park.  Several development plans indicated the land was slated for the construction of condominiums and residential homes.  The surrounding land was cleared for development in the 1950s, and charts identified the body of water as "No Name Harbor".  The plans failed, and the harbor's name was retained.

Charlotte Harbor (estuary): Charlotte Harbor Estuary, the second largest bay in Florida, is located on the Gulf of Mexico coast of west Florida, mostly (2/3) in Charlotte County, Florida with the remaining 1/3 in Lee County.  The harbor's mouth is located behind Gasparilla Island, one of the many coastal barrier islands on the southwest coast of Florida, with access from the Gulf of Mexico through the Boca Grande Pass between Gasparilla Island on the north and Lacosta Island on the south.  Charlotte Harbor covers about 270 sq mi (700 km)

Florida Keys: The Florida Keys are a coral cay archipelago located off the southern coast of Florida, forming the southernmost portion of the continental United States.  They begin at the southeastern coast of the Florida peninsula, about 15 mi south of Miami, and extend in a gentle arc south-southwest and then westward to Key West, the westernmost of the inhabited islands, and on to the uninhabited Dry Tortugas.  The islands lie along the Florida Straits, dividing the Atlantic Ocean to the east from the Gulf of Mexico to the northwest, and defining one edge of Florida Bay.  At the nearest point, the southern part of Key West is just 90 mi from Cuba.  The Florida Keys are between about 23.5 and 25.5 degrees North latitude.

Safety Harbor culture: The Safety Harbor culture was an archaeological culture practiced by Native Americans living on the central Gulf coast of the Florida peninsula, from about 900 until after 1700.  The Safety Harbor culture is defined by the presence of Safety Harbor ceramics in burial mounds.  The culture is named after the Safety Harbor Site, which is close to the center of the culture area.  The Safety Harbor Site is the probable location of the chief town of the Tocobaga, the best known of the groups practicing the Safety Harbor culture.

Operation Boot Camp: Operation Boot Camp (OBC) is a fitness boot camp founded in 2000 in Atlanta, Georgia, United States.  It is based on a physical fitness and health concept that was first conceived at Atlanta Kick, a martial arts academy in Atlanta.  In 2008, Operation Boot Camp became the largest boot camp programs of its kind in the United States.  The OBC fitness program is currently offered in Alabama, California, Georgia, Florida, Colorado, Maryland, North Carolina, Oklahoma, South Carolina, and Tennessee.  The organization teaches participants how to achieve a healthy lifestyle through a structured fitness program, personal motivation and a food plan.  The thirty-day program demands personal accountability and although it eliminates the most unpleasant aspects of recruit training and military boot camp, it is nonetheless a rigorous undertaking Like its military namesake Operation Boot Camp seeks to build confidence, strength and physical stamina.  Participants are challenged to push the boundaries of their endurance in order to reach their fitness and health goals.  The program is simple and intense and strives to teach and build new habits and to provide its boot camp participants with some fun along the way.  Operation Boot Camp recruits come from all over the world to be poked, pushed and challenged.  The staff monitors attendance and progress and provides constant feedback.  On days when the OBC members do not meet or workout with the staff they are given a list of numerous options for activities, classes and ideas to keep them active and engaged.

Harbor Defenses of New York: The Harbor Defenses of New York was a United States Army Coast Artillery Corps harbor defense command.  It coordinated the coast defenses of New York City from 1895 to 1950, beginning with the Endicott program, some of which were located in New Jersey.  These included both coast artillery forts and underwater minefields.  The command originated circa 1895 as an Artillery District(s) and became the Coast Defenses of Eastern New York and Coast Defenses of Southern New York in 1913.  Circa 1915 the Coast Defenses of Sandy Hook separated from the latter command.  In 1925 the commands were renamed as Harbor Defense Commands, and in 1935 the Harbor Defenses of Eastern New York was disestablished, although possibly retaining the minefield capability.  The remaining commands were unified as the Harbor Defenses of New York circa 1942.

Cayo Costa State Park: Cayo Costa State Park is a Florida State Park on Cayo Costa (formerly known as La Costa Island (Padilla Rancho), which is directly south of Boca Grande (Gasparilla Island), 12 mi west of Cape Coral and just north of North Captiva Island.  The park is accessible only by charter boat (with or without captain), private boat, ferry or helicopter.  Exploration of the New World by Spaniards brought traders to the west coast of Florida to barter with the Indians as early as the 17th century.  In their wake came men who started fish ranches on the out islands like Cayo Costa before Florida was opened to American settlers.  In the 1870s, Tervio Padilla, a wealthy merchant from the Canary Islands, came to Key West and established trade with natives and “ranchos” that extended northward to Charlotte Harbor.  His ships often made port at Cayo Costa at the entrance to the harbor.  Enchanted by the tropical island, he eventually decided to settle there.  Padilla prospered until the outbreak of the Spanish–American War when his fleet was burned and scuttled.  He then turned to another means of livelihood – fishing.  When the government claimed his land he was disinclined to set up another ranch so moved with his wife further down the island and as before, simply homesteaded.  For many years Charlotte Harbor locals referred to the Island as "Padilla Rancho" or Padilla Ranch although Mr. Padilla only occupied one part of the Island at a time.  Most Padilla descendants now reside in nearby Bokeelia or Boca Grande.

Boot Key: Boot Key is an island in the middle Florida Keys located adjacent to Key Vaca.  Boot Key is within the city limits of Marathon, Florida, United States.  The island is largely undeveloped despite having a bridge spanning Boot Key Harbor to Key Vaca, which is now closed to pedestrian and vehicular traffic.

Supporting paragraphs: Boot Key Harbor Florida Keys
Answer: southern coast