San Juan Bay

San Juan Bay (Spanish: Bahía de San Juan) is a semi-enclosed bay, estuary, and harbor connected to the North Atlantic Ocean in the northeastern coastal plain of the main island of Puerto Rico. Surrounded by the capital municipality of San Juan and adjacent municipalities within its metropolitan area, namely Guaynabo, Cataño, and Toa Baja, the bay is home to Port of San Juan, the primary seaport in the archipelago and island. About 3.5 miles (5.6 km) in length and 0.55 to 2 miles (0.89 to 3.22 km) in width, it is the largest body of water of several interconnected lagoons, channels, rivers, and creeks in the San Juan Bay Estuary, which covers about 83 square miles (215 km²) of land and 14 square miles (36 km²) of water in the San Juan metropolitan area in northeastern Puerto Rico.

Named after John the Baptist, whose name explorer Christopher Columbus gave to the main island of Puerto Rico as San Juan Bautista (Saint John Baptist) upon its discovery during his second vovage in 1493, San Juan Bay was first discovered and explored by Spanish conquistador Juan Ponce de León, who began the European colonization of the archipelago along its shorelines.

In 1508, Ponce de León established the city of Caparra, also called Ciudad de Puerto Rico (City of Rich Port), in the southern side of the Bay, currently part of the Pueblo Viejo barrio of the Guaynabo municipality. In 1521, his city was transferred to San Juan Islet in the northern side of the Bay under the name of San Juan Bautista de Puerto Rico (Saint John Baptist of Rich Port), today the Old San Juan historic quarter in the San Juan capital municipality. The entrance to the bay is guarded by the El Morro fortress in Old San Juan and the El Cañuelo fort in Isla de Cabras in the Palo Seco barrio of the Toa Baja municipality.