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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 the Atascosa River
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 2000, TCEQ water quality data showed elevated levels of fecal coliform bacteria and low concentrations of dissolved oxygen in 11 streams in south central Texas.

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. TCEQ worked with four river authorities and other regional stakeholders during assessment of the affected streams.

In Phase 1 of the project, TCEQ carried out targeted monitoring to collect more data about the extent and severity of the impairments in the affected streams. Results of the data analysis for each water body and parameter pair are provided in the documents linked under Phase I below. 

In Phase II, TCEQ carried out further assessment to determine appropriate management strategies for four of the streams—Elm Creek, Sandies Creek, the Atascosa River, and Mid Cibolo Creek. The remaining six segments were found to be meeting the dissolved oxygen and bacteria criteria in the Texas Surface Water Quality Standards in the Phase I analyses.

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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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Contact the TMDL Program

Please email tmdl@tceq.texas.gov, and mention the South Central Texas project in the subject line. Or call us at 512-239-6682.

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