Understanding the San Antonio River Basin

The San Antonio River Basin is a dynamic ecosystem with rivers, creeks and streams that can quickly be impacted by rain events and other weather conditions. Human activities within the basin may also affect water conditions.

The San Antonio River Basin drains an area of land 4,180 square miles. The basin extends from Kerr and Medina counties in the Texas Hill Country southeast toward the Gulf of Mexico. It drains approximately half of Medina County to the far northwest; the majority of Bexar, Wilson, and Karnes counties, which comprise the central portion of the basin; approximately one third of Goliad County to the southeast; and parts of Bandera, Kendall, Comal, Guadalupe, DeWitt, Kerr, Atascosa, Victoria and Refugio counties.

The basin’s major watersheds are

  • Medina River Watershed
  • Leon Creek Watershed
  • Upper San Antonio River Watershed
  • Salado Creek Watershed
  • Cibolo Creek Watershed
  • Lower San Antonio River Watershed

The map below shows how these watersheds drain toward the Gulf of Mexico.

The San Antonio River is the basin’s major river, flowing 240 miles from its headwaters in San Antonio, Bexar County, to its confluence with the Guadalupe River in Refugio County. Approximately 11 miles downriver of the confluence, the Guadalupe drains into the San Antonio Bay and the Gulf of Mexico.

As with all river basins, weather conditions in one part of the San Antonio River Basin can dramatically affect river flow in another part of the basin. Weather conditions may be sunny and warm in the central or southeastern part of the basin, but if rain or flood events have occurred upstream within the past few hours—or even days, paddlers, hikers, campers, and others recreating along a river, creek, or stream could be subject to the dangers of rising waters. Recreationists planning for a paddling trip in Goliad County, for instance, may find it helpful to know if recent heavy rains have occurred upstream in the San Antonio area. The river in Goliad County will have an increased flow within 2½ to three days of a heavy rain in San Antonio. Click on these links for flow information and weather conditions throughout the San Antonio River Basin