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Oso Bay and the Laguna Madre: Assessing the Aquatic Life Use

A completed project to assess low dissolved-oxygen conditions in Oso Bay and Laguna Madre

Oso Bay
Oso Bay

Counties: Cameron, Kenedy, Kleberg, Nueces, Willacy
Parameter: Dissolved oxygen
Basins: Bays and Estuaries, San Antonio–Nueces Coastal Basin, Nueces River Basin, Nueces–Rio Grande Coastal Basin
Segments: 2485, 2491

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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 receives fresh water from Oso Creek, a stream whose flow is dominated by permitted discharges, and exchanges salt water with Corpus Christi Bay. Ecologically, Oso Bay provides habitat for many plants and animals, and plays an influential role in water purification and storm protection.

The Laguna Madre is one of only five hypersaline or negative estuaries in the world. The Laguna is a shallow, bar-built coastal lagoon with limited freshwater inflow and a surface area at mean high tide of 729 square miles. The Arroyo Colorado is primarily responsible for freshwater inflow to the lower Laguna Madre. Ecologically, the Laguna is characterized as exhibiting hypersaline conditions, barren shorelines with extensive wind-tidal flats, extensive submerged seagrass meadows, and a highly productive finfishery.

Water quality testing found that concentrations of dissolved oxygen are sometimes lower than the criterion established to assure a healthy aquatic ecosystem. 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 dissolved-oxygen levels which may harm fish and other aquatic organisms.

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The TCEQ’s TMDL Program assessed concentrations of dissolved oxygen and their effect on aquatic life in the two water bodies. Based on those results, the Standards Team prepared a use attainability analysis (UAA) for the bay.

In 2010, the TCEQ proposed revisions to the site-specific standards for dissolved oxygen in the bay. The EPA rejected those revisions as not adequately supported by the documentation. The Standards Work Group then carried out additional assessment to support a change in the standards. Additional revisions were submitted in 2014 and 2018 for Oso Bay, Upper Laguna Madre, and Blind Oso Bay. These revisions are pending EPA approval. E-mail the Standards Team for more information about the Standards revisions.

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For More Information

Please send an e-mail to and mention the Oso Bay and Laguna Madre project in the subject line. Or call us at 512-239-6682.

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