The Medina River is located in south central Texas

Texas

Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...

, USA, in the Medina Valley

Medina Valley

Medina Valley, also known as the Medina River Valley, is an area in south central Texas containing the Medina River, Lake Medina and the Medina Dam. It serves to drain the Balcones Escarpment of the Texas Hill Country and irrigate the farms contained therein...

. Named after Pedro Medina, a Spanish engineer, by Alonso de León

Alonso De León

Alonso de León wasexplorer and governor, who led several expeditions into the area that is now northeastern Mexico and southern Texas.-Early life:...

, Spanish governor of Coahuila

Coahuila

Coahuila, formally Coahuila de Zaragoza , officially Estado Libre y Soberano de Coahuila de Zaragoza is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico...

, New Spain

New Spain

New Spain, formally called the Viceroyalty of New Spain , was a viceroyalty of the Spanish colonial empire, comprising primarily territories in what was known then as 'América Septentrional' or North America. Its capital was Mexico City, formerly Tenochtitlan, capital of the Aztec Empire...

 in 1689. It was also known as the Rio Mariano, Rio San Jose, or Rio de Bagres (Catfish river). It once served as the official boundary between Texas and Coahuila with the San Antonio River

San Antonio River

The San Antonio River is a major waterway that originates in central Texas in a cluster of springs in north central San Antonio, approximately four miles north of downtown, and follows a roughly southeastern path through the state. It eventually feeds into the Guadalupe River about ten miles from...

 being considered its tributary. At that time, the river was called the Medina all the way to the Gulf of Mexico

Gulf of Mexico

The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...

, but now the part below the confluence is called the San Antonio River. It starts in springs in the Edwards Plateau

Edwards Plateau

The Edwards Plateau is a region of west-central Texas which is bounded by the Balcones Fault to the south and east, the Llano Uplift and the Llano Estacado to the north, and the Pecos River and Chihuahuan Desert to the west. San Angelo, Austin, San Antonio and Del Rio roughly outline the area...

 in northwest Bandera County, Texas

Bandera County, Texas

Bandera County, formed in 1856 from Bexar and Uvalde counties, is a county located on the Edwards Plateau in the U.S. state of Texas. As of 2000, the population is 17,645. Its county seat is Bandera. Bandera is named for the Spanish word for flag...

 and merges with the San Antonio River in southern Bexar County, Texas

Bexar County, Texas

As of the census of 2000, there were 1,392,931 people, 488,942 households, and 345,681 families residing in the county. The population density was 1,117 people per square mile . There were 521,359 housing units at an average density of 418 per square mile...

, for a course of 120 miles. It contains the Medina Dam

Medina Dam

The Medina Dam is a hollow-masonry type dam built in 1911 and 1912 by the Medina Irrigation Company in what became Mico, Texas. Medina Lake extends north of it in northeastern Medina County, Texas. The dam and irrigation project was designed and financed by Dr. Frederick Stark Pearson, an American...

 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.

Natural features

Much of the source water to the Medina River is produced by springs emerging due to the presence of the Balcones Fault

Balcones Fault

The Balcones Fault Zone is a tensional structural system in Texas that runs approximately from the southwest part of the state near Del Rio to the north central region near Waco along Interstate 35. The Balcones Fault zone is made up of many smaller features, including normal faults, grabens, and...

. This locale of the Balcones Fault is associated with an important ecological dividing line for species occurrence. For example, species such as the California Fan Palm, Washingtonia filifera

Washingtonia filifera

Washingtonia filifera , with the common names California Fan Palm , Desert Fan Palm, Cotton palm, and Arizona Fan Palm. It is a palm native to southwestern North America between an elevation range of , at seeps, desert bajadas, and springs where underground water is continuously available...

, occur only west of the Medina River or Balcones Fault.

The Medina River once received significant waste discharge from upstream catfish farming operations, which utilized more water than was sustainable to the basin's safe usage.