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South Central Texas Streams: Evaluating Water Quality for Aquatic Life and Recreation

Completed assessment project that evaluated high bacteria and low dissolved-oxygen concentrations in several streams in south central Texas and determined whether TMDLs were required

photo of sampling in the Atascosa River

Sampling in the Atascosa River

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Counties: Atascosa, Bandera, Bexar, Blanco, Comal, De Witt, Duval, Frio, Hays, Gonzales, Guadalupe, Karnes, Kendall, Kerr, La Salle, Live Oak, McMullen, Medina, Real, Travis, Uvalde, Webb, Wilson
Parameters: Bacteria, dissolved oxygen
Basins: Colorado River, Guadalupe River, Nueces River, San Antonio River
Segments: 1427, 1803A, 1803B, 1806A, 1815, 1906, 1908, 1913, 2104, 2107, 2113

Project Description

In 11 streams in south central Texas, water quality testing found elevated levels of fecal coliform bacteria and low concentrations of dissolved oxygen.

High concentrations of bacteria such as E. coli and fecal coliform, which are found in both human and animal waste, may indicate a health risk to people who swim or wade in the water body—activities called "contact recreation" in the state's standards for water quality.

Oxygen, which dissolves in water, is essential for the survival of aquatic life. While the amount of dissolved oxygen in water fluctuates naturally, various human activities can cause unusually or chronically low levels of dissolved oxygen, which may harm fish and other aquatic organisms. The TCEQ worked with four river authorities and other regional stakeholders during assessment of the affected streams.

Phase 1 of the project involved targeted monitoring to collect more data and information on the extent and severity of the impacts on water quality in the project streams. The data has been analyzed, and the results are summarized below in the overview of Phase I.

In Phase II, the TCEQ carried out further assessment to determine appropriate strategies for four of the project water bodies—Elm Creek, Sandies Creek, the Atascosa River, and Mid Cibolo Creek. Data from Phase I for the remaining six segments indicated that they were meeting their associated dissolved oxygen and bacteria criteria.

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Phase I—Overview, Documents, and Public Meetings

Phase I consisted of targeted monitoring and assessment to determine the extent and severity of the impairments, and to further characterize water quality, in order to determine if TMDLs were needed for the project segments.

Phase I—Project Reports on Impairment Verification Monitoring

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Phase II—Strategy Development

Based on the analyses of Phase I data, the TMDL Team carried out further assessment to determine the most appropriate management strategy for four of the streams.

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For More Information

Please e-mail us at, and mention the South Central Texas project in the subject line. Or call 512-239-6682.

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communities working together taking care of our rivers, lakes, and bays