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Gulf Coast Oyster Waters

This is a community project to reduce bacteria in oyster waters of the Upper Gulf Coast. The Department of State Health Services uses levels of certain bacteria as an indicator of the safety of oyster harvesting. The total maximum daily loads (TMDLs) were adopted and the implementation plan (I-Plan) has been approved. Together, they provide the road map to improved water quality.

photo of people harvesting oysters off the Gulf coast
Palacios Port Jetty in the Greater Matagorda Bay watershed

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, 2433, 2434, 2435, 2439

On this page:

Background and Goals

Bacteria concentrations are sometimes elevated in several 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), Bastrop Bay/Oyster Lake (Segment 2433), Christmas Bay (Segment 2434), Drum Bay (Segment 2435), and 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 .

The goal of this 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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Get Involved

The Galveston Bay Foundation coordinated stakeholder participation in developing the I-Plan. Work groups were formed at a public meeting on February 24, 2010 and were held regularly while the I-Plan was being developed.

To get involved with implementing the plan, visit the Galveston Bay Foundation Volunteer webpage or contact Emily Ford at

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Tracking of implementation allows stakeholders to evaluate actions taken, identify actions that may not be working, and make changes as necessary.

photo of stakeholders at public comment meeting photo of stakeholders examining maps and literature

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Implementation Plan

Stakeholders in the region developed this I-Plan. On August 19, 2015, the commission approved their plan.

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.

TMDLs for three additional segments—2433, 2434, and 2435—were added by addenda in 2012 (see below). 

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.


Revisions 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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For More Information

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

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Communities Working Together