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You are here: Home / Water Quality / Total Maximum Daily Load Program / Oso Bay: A Project to Assess the Oyster Waters Use

Oso Bay: A Project to Assess the Oyster Waters Use

A completed assessment project to determine whether bacteria levels in Oso Bay are high enough to affect oyster beds in Corpus Christi Bay.
photo of Oso Bay
Satellite photo of Oso Bay
Courtesy of the Center for Coastal Studies

County: Nueces
Parameter: Bacteria
Coastal Basins: Bays and Estuaries, Nueces–Rio Grande Coastal Basin
Segment: 2485

Background and Goals

Oso Bay is an enclosed, shallow body of water situated along the southern shore of Corpus Christi Bay, with a surface area of approximately seven square miles. The bay exchanges saltwater with Corpus Christi Bay and receives fresh water from Oso Creek.Most of the flow in Oso Creek is discharged water from permitted facilities. Ecologically, Oso Bay provides habitat for many plants and animals, and plays an influential role in water purification and storm protection.

To protect consumers, the Texas Department of State Health Services designates, monitors, and classifies shellfish harvesting areas along the Texas coast. DSHS has identified Oso Bay, Segment 2485OW, as an oyster harvesting area and classified it as restricted. Although there are no oyster beds in Oso Bay, because it empties into Corpus Christi bay, it is considered part of the larger bay’s harvesting area.

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 coastal waters. Microorganisms from human and animal waste may contaminate oysters and other shellfish, making them unsafe to eat, especially since some shellfish are eaten raw. However, DSHS restrictions are based on their estimated risk of bacterial contamination rather than on actual measurements of bacteria in oysters or oyster waters.

In response to the oyster waters restriction, the TCEQ's Total Maximum Daily Load Program gathered additional indicator bacteria data to assess water quality in the bay. The goal of the project was to determine whether the bacteria concentrations in Oso Bay exceeded the criteria for oyster harvesting.

The TCEQ and area stakeholders are also working on a TMDL for bacteria in Oso Creek and have completed a TMDL for bacteria affecting recreational uses of Oso Bay.

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Status

The final project report confirmed that Oso Bay is generally not meeting the standard for oyster water harvesting. This finding validates the risk assessment by the DSHS. Because bacteria concentrations spiked during rainfall events, stormwater runoff is the most likely source.

Two measures of bacteria were used to evaluate conditions—a median concentration over time and a percent of time the maximum concentration was exceeded. Five stations were monitored. At three of the stations, the acceptable median concentration was exceeded most of the time. At all five stations, concentrations higher than the maximum happened more than 90% of the time.

Bacteria concentrations were consistently higher than the criteria used to determine the possibility of health risks to people from eating oysters.

Next Steps

People who have a stake in changes to the watershed will decide how to move forward. Developing a TMDL will be an option to consider. Another option is to broaden their scope, since high bacteria concentrations also pose a possible health risk to people who swim or wade in Oso Bay and Oso Creek. Stakeholders are already working on two related planning projects to reduce bacteria in Oso Bay and Oso Creek. Their work, when implemented, is likely to reduce the amount of bacteria in the bay. Fewer bacteria in the water would probably reduce bacteria in oysters.

Get Involved

In all its TMDL projects, the TCEQ works with people who represent government, permitted facilities, agriculture, business, environmental, and community and private interests in the watershed. Notice of public meetings were posted on this website and in print and electronic media.

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Reports

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For More Information

Please send an e-mail to tmdl@tceq.texas.gov, and mention the Oso Bay Oyster Waters project in the subject line. Or call us at 512-239-6682.

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