The Medina River is located in south central Texas in the Medina Valley. Named after Pedro Medina, a Spanish engineer, by Alonso de León, Spanish governor of Coahuila, New Spain in 1689. It was also known as the Rio Mariano, Rio San Jose, or Rio de Bagres (Catfish river). Once it served as the official boundary between Texas and Coahuila with the San Antonio River being considered its tributary. At that time, the river was called the Medina all the way to the Gulf of Mexico, but now the part below the confluence is called the San Antonio River. It starts in springs in the Edwards Plateau in northwest Bandera County, Texas and merges with the San Antonio River in southern Bexar County, Texas, for a course of 120 miles. It contains the Medina Dam in NE Medina County, Texas which restrains Lake Medina. Much of its course is owned and operated by the Bexar-Medina-Atascosa Water District to provide irrigation services to farmers and ranches.