Croton Dam, Reservoir, and Aqueduct, part of the extensive water supply system for New York City. The reservoir, in northern Westchester county, New York, was the city’s first artificial source of water. The original dam on the Croton River, located 10 km (6 miles) upstream from that river’s confluence with the Hudson River, was the first large masonry dam in the United States (1837–42). John B. Jervis designed the granite-faced rubble structure, which still exists although it was overtopped by water impounded by the second dam (1893–1906). Also of rubble with granite facing, the later structure is 536 metres (1,760 feet) long and stands 87 metres (291 feet) above foundation level. The first aqueduct, built aboveground, was more than 65 km (40 miles) long. It was carried over the Harlem River near 173rd and 174th streets by the Aqueduct Bridge (“High Bridge”), a massive multiple-arch stone span also designed by Jervis (1839–42, 1848; largely replaced 1937), and delivered the water to an enormous receiving reservoir located at what is now the Great Lawn of Central Park. The old aqueduct was replaced by an underground aqueduct, which was built in 1885–93 and is still in use. Remnants of the original aqueduct are visible in scenic trails maintained by New York City and New York state.