The San Buenaventura Mission Aqueduct was a seven-mile long, stone and mortar aqueduct built in the late 18th and/or early 19th century to transport water from the Ventura River to the Mission San Buenaventura in Ventura, California. Accounts vary greatly as to when the aqueduct was built. One account indicates it was built between 1780 and 1790 by the Chumash Indians under the direction of a Spanish priest trained in hydrology. Others place its construction in the 1790s, and yet another indicates it was built between 1805 and 1815 by stonemasons brought from Mexico.