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Tidal Streams: Evaluating Water Quality for Support of Aquatic Life

A completed project to assess appropriate dissolved oxgyen criteria for support of aquatic life in tidal streams
photo of a tidal portion of Aransas River
Aransas River Tidal

Parameter: Dissolved oxygen
River Basins: San Antonio-Nueces Coastal, Nueces-Rio Grande Coastal (Phase II); Bays and Estuaries, Sabine River, Colorado-Lavaca Coastal (Phase I)
Segments: 2001, 2003, 2201, 2301 (Phase II); 0511, 1501, 2453A (Phase I)
Counties: Refugio, San Patricio, Willacy, Cameron (Phase II); Jackson, Matagorda, Orange, Victoria (Phase I)

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Background and Goals

Tidal streams are highly productive transitional areas between the freshwater of rivers and the salt water of bays. Tidal streams serve as nurseries for many fish and shellfish, including several species important for commerce and recreation.

Routine monitoring of several tidal streams revealed dissolved oxygen measurements that were not meeting water quality standards. Dissolved oxygen is essential to the survival of fish and other aquatic life. Prior studies led to questions concerning the appropriateness of current dissolved oxygen criteria, because tidal systems are naturally quite variable over space and time.

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Phase I of this project, completed in 2007, focused on the tidal portions of three streams—Cow Bayou (Segment 0511) on the upper Texas coast, and Tres Palacios Creek Tidal (Segment 1501) and Garcitas Creek Tidal (Segment 2453a) on the middle coast. At present, no generally accepted method exists for determining the health of aquatic communities in tidal streams. This project was planned to aid in developing such a methodology by studying the biological, chemical, and physical characteristics of the streams in question.

Results and lessons learned during Phase I of the project were then applied to the study of additional tidal streams along the Texas coast in Phase II of the project. New data were collected on the tidal portions of two streams—Mission River Tidal (Segment 2001) and Aransas River Tidal (Segment 2003). In addition, the statistical methods employed in assessing these water bodies were applied to at least seven existing data sets from other tidal streams in Texas.

Phase II was completed in November 2011. The final report was submitted to the TCEQ Standards Team for use in evaluating the appropriate dissolved oxygen criteria for support of the aquatic life use in tidal streams.

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Phase II Information

Documents are provided in PDF.

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Phase I Information

Documents are provided in PDF.

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For More Information

Please e-mail us about this project at, and mention the Tidal Streams Uses project in the subject line. Or call us at 512-239-6682. To find out about the standards for tidal streams, please e-mail

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