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You are here: Home / Water Quality / Total Maximum Daily Load Program / Upper Gulf Coast: A TMDL Project for Bacteria in Oyster Waters

Upper Gulf Coast: A TMDL Project for Bacteria in Oyster Waters

A project to develop and implement TMDLs that reduce bacteria in oyster waters. The Department of State Health Services uses levels of certain bacteria as an indicator of the safety of oyster harvesting. The TMDLs have been adopted, and the stakeholders are developing an implementation plan, which will provide the road map for improving water quality.
photo of
Oyster Harvesting in the
Gulf of Mexico

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Counties: Brazoria, Chambers, Galveston, Harris
Parameter: Bacteria in Oyster Waters
Basins: Neches-Trinity Coastal, Trinity River, San Jacinto River, and San Jacinto–Brazos Coastal, Bays and Estuaries
Segments: 2421, 2422, 2423, 2424, 2432, 2439

Background and Goals

Bacteria concentrations are sometimes elevated in six bays in the Houston–Galveston area. Restricted areas are closed to the harvesting of shellfish for direct marketing. Microorganisms from human and animal waste may contaminate oysters and other shellfish, making them unsafe to eat, especially since some shellfish are eaten raw.

The use of coastal waters for harvesting shellfish —called the “oyster waters use” in the state’s standards for surface water quality—is the most commonly impaired use among Texas bay and gulf waters. The affected segments are Upper Galveston Bay (Segment 2421), Trinity Bay (Segment 2422), East Bay (Segment 2423), West Bay (Segment 2424), Chocolate Bay (Segment 2432), Lower Galveston Bay (Segment 2439).

Assessment of the oyster waters use is conducted by the Seafood Safety Division of the Texas Department of State Health Services. The DSHS is responsible for monitoring and classifying shellfish harvest areas into four categories for harvesting—approved, conditionally approved, restricted, or prohibited. These classifications are published as maps on the DSHS website Exit the TCEQ.

The goal of this TMDL project is to improve water quality so that the oyster beds are routinely safe for harvesting. Analysis indicates that isolated zones of high bacteria concentrations occur in isolated areas near shorelines, rather than occurring chronically throughout the bays. Because the exceedances are confined to discrete areas, bay-wide reductions can be achieved by targeting each isolated zone.

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Implementation Plan

An I-Plan describes the steps the TCEQ and partners will take to achieve the pollutant reductions identified in the TMDL report. See an overview of the plan development process.

The Galveston Bay Foundation (GBF) is coordinating stakeholder participation in developing the I-Plan (see Participate" below). Stakeholders submitted a draft I-Plan for TCEQ technical review in early 2014.

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Total Maximum Daily Loads

On August 20, 2008, the commission adopted the six original TMDLs below. On February 4, 2009, the EPA approved these TMDLs, at which time they became part of the state’s Water Quality Management Plan.

  • Six Total Maximum Daily Loads for Bacteria Adobe Acrobat PDF Document in Waters of the Upper Gulf Coast, Segments 2421, 2422, 2423, 2424, 2432, and 2439
    (Includes an amendment in Appendix that gives the median fecal coliform capacity of the restricted oyster-water assessment units; this also serves as Addendum 1 to the original document.)
  • Response to Public Comment Adobe Acrobat PDF Document on the TMDLs

Revisions to TMDLs

From time to time, it is necessary to revise TMDLs to account for changing conditions in the watershed. Revisions to the load allocations in TMDLs are made via the state’s Water Quality Management Plan (WQMP), which is updated quarterly.

The WQMP provides projected effluent limits for use in planning and permitting activities under the Texas Pollutant Discharge Elimination System (TPDES). The TCEQ reviews all applications for new and amended permits for conformance with applicable portions of the WQMP, including adopted TMDLs.

Revisions are made to TMDLs in one of two ways:

  • Updates are made to account for changing conditions in the watershed, such as new or revised wasteload allocations, permits that have been canceled or have expired, or changed facility names.
  • Addenda are created to add load allocations for assessment units that are impaired by the same pollutant or condition, within the same watershed as in the original TMDL report.

Both updates and addenda are provided in the same units of measure used in the original TMDL.


Additional TMDLs for the Upper Texas Coast have been added by addenda:.

The reductions of bacteria loads were completed using a concentration-based approach, which compares water quality to both the median and the 90th percentile criteria for acceptable concentrations.


Updates to the TMDL are documented in the approved WQMP updates listed below.

Learn more about WQMP updates and about opportunities to comment on revisions to them.

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The TCEQ is working with existing forums in the watershed to inform the public about the project and work together with stakeholders on an IPlan to improve conditions in the watershed.

The Galveston Bay Foundation Exit the TCEQ is coordinating stakeholder participation in developing the I-Plan. Work groups were formed at a public meeting on February 24, 2010. These work groups are developing sections of the I-Plan.

The Foundation hosted three meetings in July 2010 to share progress on I-Plan development and the draft management measures developed by each work group.

For additional information about the work group meetings or to get involved, visit the Galveston Bay Foundation Exit the TCEQ website.

Summaries of Meetings during TMDL Development

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Project Documents

1905 Map of Galveston Bay:

This 1905 map of Galveston Bay (JPG, 9.9 MB) was originally produced by the Corps of Engineers. An old paper copy, the only known copy of this map, was scanned to produce digital images.

The file posted here was made by combining two overlapping partial images, merging to a single image, adjusting color to reduce yellowed effect of original, trimmed, and reduced to 4000 x 4000 pixel density to make a smaller but readable image.

Larger format (6848 x 9584 pixels) files are available in TIF and JPG format, but require additional work to merge pieces or color correct the image. Contact us (see below) if you want the original files.

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For More Information

Please e-mail us at, and reference the Upper Coast Oyster Waters TMDL in the subject line. Or call us at 512-239-6682.

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