The San Antonio River rises in a cluster of springs in north central San Antonio (in central Bexar County) approximately four miles north of downtown (at 29° 28' N, 98° 29' W). Olmos Creek empties into the river just below its head, and other springs continue to join as the river flows through the city. From San Antonio, the river flows southeast 180 miles through Wilson, Karnes, and Goliad counties and then forms the county line between Victoria and Refugio counties. It empties into the Guadalupe River four miles north of Tivoli at the intersection of the Calhoun, Refugio, and Victoria county lines (at 28° 30' N, 96° 53' W). Along its course the river traverses flat to gently rolling terrain surfaced by clay and sandy loams that support mesquite, live oak, cacti, and grasses. The spring flow of the San Antonio and its principal tributaries, the Medina River and Cibolo Creek, makes the volume of the river steadier than that of most Texas streams. The San Antonio River is dammed to form two artificial reservoirs in the San Antonio area. One near the head of the stream, impounded by Olmos Dam, has a capacity of 15,500 acre-feet and is used solely for flood control. The other reservoir, Lake Blue Wing, ten miles south of San Antonio, has a capacity of 1,000 acre-feet and is used for irrigation.
The San Antonio has been identified as one of the rivers crossed by Álvar Núñez Cabeza de Vaca in his journey across Texas in 1535 and as the stream called Arroyo De León by Alonso De León on his fourth expedition into Texas in 1689. The stream was named for San Antonio de Padua on June 13, 1691, by Domingo Terán de los Ríos, who was on an inspection tour with Father Damián Massanet to the East Texas missions. At the site of present-day San Antonio they found an Indian village, which they understood the Indians to say was named Yanaguana. Father Massanet renamed the village San Antonio de Padua and offered a Mass for the soldiers and Indians gathered there. In 1709 Father Antonio de San Buenaventura y Olivares was so impressed with the location that he wanted to establish a mission there. He petitioned for permission at least as early as 1716, and on May 1, 1718, San Antonio de Valero Mission was established on the east bank of the river. On May 5, San Antonio de Bexar Presidio was set up on the opposite side of the stream. The plentiful supply of water for drinking, irrigation, and water power caused the San Antonio River rapidly to become the center of Spanish activities in the province of Texas. Other missions established in the immediate vicinity were San José y San Miguel de Aguayo and San Francisco Xavier de Náxara. In 1731 the villa of San Fernando de Bexar, which developed into the modern city of San Antonio, was founded. The same year, three missions were moved from East Texas to the San Antonio River and renamed Nuestra Señora de la Purísima Concepción de Acuña, San Francisco de la Espada, and San Juan Capistrano. In 1749 Nuestra Señora de Loreto Presidio and the Nuestra Señora del Espíritu Santo de Zúñiga Mission were moved from the Guadalupe to a site on the San Antonio River that later became the town of Goliad. Another mission, Nuestra Señora del Rosario, was established about four miles upstream in 1754. The river was likewise popular with the colonial empresarios of the Mexican period, and much of the land bordering the stream was granted to colonists in the De León and Power and Hewetson colonies. When the Texas Revolution began, the river became the scene of heroic and catastrophic engagements, including the battle of Concepción, the Grass Fight, the siege of Bexar, the Goliad Massacre, and the battle of the Alamo.
Although the San Antonio River has furnished drinking and irrigation water as well as power to turn the wheels of mills, foundries, and tanneries, in recent times it has been most significant for its beauty. In the city of San Antonio, where it is spanned by more than fifty bridges, this unhurried stream runs fifteen miles across six miles of city blocks. In 1939 a $300,000 river-beautification project, financed by a city bond issue and a Work Projects Administration grant, was inaugurated. The river was made a pedestrian thoroughfare flanked by walks from all principal downtown streets. It was deepened so it would be navigable for small craft. The project included landscaping, fountains, and the construction of an outdoor theater equipped with water curtains. The network of walkways and bridges, now known as the Paseo del Rio or Riverwalk, is one of San Antonio's principal attractions. It was enhanced and extended during HemisFair '68. The old Spanish town known as La Villita has also been restored and has become one of the showplaces of the San Antonio River area.