Key Vaca is an island in the middle Florida Keys, located entirely within the borders of the city of Marathon, Florida. Geography Key Vaca is located in between Fat Deer Key and Knight's Key. Vaca Key was also connected via bridge to Boot Key until the city of Marathon neglected the bridge so long it had to be torn down causing hardships to the business on Boot Key. Key Vaca comprises most of the north shore of Boot Key Harbor. Nomenclature Various theories as to the origin of the name exist. The most likely example is that the island was named after Álvar Núñez Cabeza de Vaca, who wrote a detailed account of the 16th-century exploration of Florida. Other theories revolve around the word vaca, meaning "cattle" in Spanish. The 1957 book The Florida Keys indicates that the island's name comes from wild cattle that used to live on the island. Evidence of these cattle has never been found. The name may also refer to manatees, "sea cows" that thrived in the area prior to the 1950s. Because it lies completely within the borders of Marathon, the island is often incorrectly referred to as "Marathon Key". Climate Key Vaca is located geographically in the subtropics, but with a completely tropical climate. Because of the proximity of the Gulf Stream to the southeast, and the tempering effects of the Gulf of Mexico to the west and north, Key Vaca has a notably mild, tropical-maritime climate, (Köppen climate classification Aw, similar to the Caribbean islands). Cold fronts are strongly modified by the warm water as they move in from the north in winter. The average low and high temperatures in January are and . In the summer, temperatures are somewhat higher than in Key West, due to the island's proximity to the shallower waters of Florida Bay, which are heated more easily than the deeper waters of the Florida Strait, south of Key West. The season is characterized by hot, humid conditions and sharp, sudden thunderstorms that often drop substantial amounts of rain on the island. Hurricanes are a common threat during the summer, and sometimes affect the island directly, as was the case with the Labor Day Hurricane of 1935, Hurricane Donna in 1960, Hurricane Wilma in 2005 and most recently, Hurricane Irma in 2017. The average low and high temperatures in August are and , with temperatures sometimes approaching the