The Medina River rises in north and west prongs that originate in springs in the Edwards Plateau divide of northwest Bandera County and converge near Medina (at 29°48' N, 99°15' W). The river then flows southeast for 116 miles to its mouth, on the San Antonio River in south Bexar County (at 29°14' N, 98°24' W). The first European to see the river was Alonso De León, governor of Coahuila, who led his expedition across Texas in 1689 in pursuit of the French. De León noted in his diary that he named the stream for Pedro Medina, the early Spanish engineer whose navigation tables he was using in mapping his route through the wilderness with an astrolabe. On other old maps the river is designated variously as Río Mariano, Río San José, or Río de Bagres—Catfish River. For a time it was considered the official boundary between Texas and Coahuila and shown as running to the Gulf of Mexico, with the San Antonio River labeled as a tributary. Later the designations were reversed, and, along with Cibolo Creek, the Medina has been regarded as a tributary of the San Antonio. On August 18, 1813, bearers of the green flag of the Republican Army of the North, fighting to uphold the declared independence of Mexico from Spain, met defeat in the battle of Medina at the river southeast of San Antonio de Béxar. Hundreds of rebel troops were killed by forces under Spanish general Joaquín de Arredondo. At the same site on March 2, 1836, Gen. Antonio López de Santa Anna paused in his march from the Rio Grande in order to gather forces for the final approach to Bexar and the engagement with Texans in the Alamo. Diarist José Enrique de la Peña mentions resting at the river, the making of plans, and carrying out such tasks as assigning horses to dragoons. In the midst of the excitement over impending battle, Peña still took note of "the little stream whose banks were rich with pecan trees."
A decade later, the same stream, with its gallery of pecan and cypress, caught the attention of European empresario Henri Castro as he negotiated contracts to bring colonists to the new Republic of Texas. Castro chose a site at a bend of the river to lay out a town to serve outlying farms of immigrants from Alsace and nearby German states. The first band of colonists, though beset with many difficulties, arrived in 1844 to begin building Castroville. Efforts on the part of Castro and his principal partner, A. F. Louis Huth, continued for some years to recruit additional groups and individuals to the Medina valley. With success made difficult by the alternation of drought and flood typical of the Balcones Fault zone of Texas, Castro is reportedly the first to have envisioned a dam on the box canyon of the river to impound floodwater for irrigation of the fertile fields below. Near the site of the later Medina Dam, an earthen dam was built in 1850, which was soon replaced by a stone structure providing power for a downriver mill.
From San Antonio and the outpost of Castroville, enterprising small bands of shingle makers and charcoal burners began working their way up the river, taking advantage of abundant timber and the protection from Indian danger provided by the Texas Rangers. There were several families camping on the river in the late 1840s at the horseshoe bend later chosen as the townsite of Bandera. Arriving in 1854 was a band of Mormons who had traveled to Texas after breaking away from the Utah-bound main group. They settled at Fredericksburg before moving on to the Medina; the group moved again from Bandera and finally established itself downriver at Mountain Valley. Till the death of leader Lyman Wight, the group remained intact and engaged in the manufacture of lumber and furniture.
In 1852 John James, Charles Demontel, and John Herndon formed a partnership for the purpose of building a cypress-lumber mill and laying out a town "on the Medina above Castroville." Their plan, implemented the following year, involved a site at the deep bend already occupied by the shingle camps. Sixteen Polish families from Upper Silesia, originally members of the Polish colony in Karnes County, were hired to build and work the mill; they arrived in 1855. Government contracts for lumber and shingles to be used in the construction of cavalry posts across the Southwest kept the enterprise going until floods during the 1870s destroyed the mill and all other development at river level. During the years of the great cattle drives to the Midwest, herds from South Texas followed the Medina River to converge at gathering pens around the Bandera area before heading north on the Western Trail. A large operation was carried on at Ten-Mile Crossing by Louis Schorp and the brothers John and Joseph Spettel. Other local ranchers and merchants also entered into the business of contracting to move cattle to northern markets. The availability of water from the Medina and its many spring-fed small tributaries seems to have determined the choice of Bandera as a staging area for cattle drives.
The well-known recurrence of the floods that had destroyed the lumber industry revived the idea of a major dam in the famous box canyon of the Medina. Alex Walton, who had visited the canyon in 1894, interested fellow engineers Frederick Stark Pearson and Clint Kearny in launching a project to build such a dam, with canals to carry irrigation water to highly promoted farm tracts in the lower Medina valley around Natalia. A company was formed, assisted by investment of British capital, and the scheme was brought slowly to fruition, despite drought and financial disaster. After construction of the concrete dam was finished in 1912, the proposed lake stood dry until rains a year later brought water down the river. The subsequent spate of settlers spurred the intended agricultural enterprises as well as the construction of summer homes and fishing resorts. Youth camps and dude ranches also proliferated around the lake and along the river upstream.
The river and the lake suffered through record dry periods in the 1930s and the 1950s, which were followed by the usual floods. On August 2, 1978, what was widely termed a 500-year flood came down the Medina, an unofficial record rainfall of forty-eight inches having fallen on the North Prong in twenty-four-hours. Twenty-two lives were lost, millions of dollars of property loss or severe damage reported, and thousands of cypress and pecan trees downed. After a cleanup program by the United States Army Corps of Engineers and private contractors, strict floodplain regulations were ordered to be enforced by the Federal Emergency Management Agency. More sophisticated rainfall reporting and warning systems than those previously in place were put into effect.
As of 1990 proposals were being made by the Edwards Underground Water District for purchase of water rights of members of the Bexar-Medina-Atascosa Water District, the successor to the original Medina Lake irrigation project. The water purchased would be diverted into the Edwards Aquifer by way of injection wells below the dam. At the same time, upstream use of water was being put under the jurisdiction, for the first time, of a water master appointed by the Texas Water Commission. Preliminary work was also underway to build a second large dam on the Medina River. The Applewhite Reservoir, a subject of controversy and litigation on the part of opponents, was to provide a surface-water supplement to the underground Edwards Aquifer and the metropolitan area of San Antonio and surrounding counties.